Glossary of Automotive Terms – H

Letter H – Dictionary of Automotive Terms

  1. A letter rating for tires to indicate that they are theoretically rated for speeds up to 210 kph (130 mph), as in P185HR13. The next higher rating is V and the one lower rating is T.
  2. Système International (SI) symbol for Henry
  3. Symbol for Hydrogen
Abbreviation for Water
Abbreviation for High Altitude Compensator
Hackney Carriage
Black taxis in London.


A tool for cutting metal, with a narrow blade attached to a frame

  1. Abbreviation for Heated air inlet system
  2. Abbreviation for hot air intake
Hairline crack
A tiny stress crack which forms due to strains in the material or extreme temperature differences; as opposed to crazing, a single crack of this type will often occur alone
Hair pin

Hair pinHair pin

A roadway with several sharp turns usually on an hill.

Hair pin cotter

Hair pin cotterHair pin cotter

A securing device shaped somewhat like a U in which the legs have a series of waves or bends. Insert one leg into the hole of a rod so that the bent leg will encircle the rod.


Hairpin valve spring
A valve spring formed from a wire or metal strip bent to form two levers emanating from a half-loop or coil; used on some classic cars and motorcycles
Abbreviation for Heated Air Intake System (Chrysler)
Half dog point
The same as a dog point but half as long; used on short screws for the same purposes as the dog point, but in a shallower hole or slot.
Half dog point socket set screw
A headless socket set screw threaded the entire length. It has a hexagonal drive at one end and a protruding tip with a flat surface at the other end.
Half link

Half linkHalf link

Every chain has rollers which are connected by side plates or Keepers. When counting the number of links in a length of chain, it is easiest to count the number of side plates on one side of the chain and multiplying the number by two. When a chain needs to be an odd number, a half link is included. The term half link is a misnomer. It should be called a single link. The side plate on a half link is not flat but has a step down shape. For this reason, it is called an offset link.

Half moon key
Half-moon key

Half-moon keyHalf-moon key

A driving key serving the same purpose as the regular key but it is shaped somewhat like a half circle. Also called a Woodruff key.

Half-moon slip joint pliers
A multiple-slip joint pliers with groove joint
Half-round body file
A body file with domed file surface for working reverse-crowned panels
Half-round file
A special file that’s flat on one side and convex on the other
Half shaft
A rotating shaft that transmits power from the final drive unit to one side of the drive wheels, but usually refers to the two shafts that connect the road wheels to the final drive with Independent rear suspension or Front-wheel drive as opposed to the axle shafts of a live rear axle. Also called an Axleshaft
Half step gearing
Half-step gearing
A Gearing system of a bicycle in which a shift between chainrings in a double chainring set is equivalent to half a gear step on the freewheel.


Vehicle with caterpillar tracks over the rear wheels to provide motive power but steered by normal front wheels

Half wave rectifier
A rectifier which blocks one-half of an ac sine wave to convert ac into dc.


Half-wave rectifier
A rectifier which blocks one-half of an ac sine wave to convert ac into dc.


Halide Lamp
Halide refrigerants
Family of refrigerants containing halogen chemicals.
Halide torch
Type of torch used to safely detect halogen refrigerant leaks in system.
Hall effect
In electrical conductors where electric current flows perpendicular to a magnetic field, a so-called Hall voltage is produced perpendicular to the direction of current flow and to the magnetic field

Hall-effect ignition system
Transistorized ignition with Hall generator
Hall-effect sensor
A Hall generator
Hall-effect switch
A Hall vane switch
Hall element
A pulse generator that makes use of the Hall effect and consists of a rotor with vanes, a conductive element with a permanent magnet and the Hall IC. Also called Hall generator. When the air gap is unobstructed, a Hall voltage is generated; when a vane stands in the air gap, the magnetic flux cannot reach the Hall IC. Hall generators used as ignition pulse generators have as many vanes and Hall windows as the engine has cylinders, dwell being determined by the width of the vanes. Hall generators used in electronic-map ignition systems to provide the engine starting signal have only one Hall window
Hall generator
A pulse generator that makes use of the Hall effect and consists of a rotor with vanes, a conductive element with a permanent magnet and the Hall IC. Also called Hall element.

Hall IC
A solid state device with the actual Hall generator and integrated circuits for voltage amplification and potential reversal, producing the pulses for the control unit
Hall module
A Hall IC
Hall sensor
A Hall generator.

Hall vane switch
A switch that makes use of the Hall effect. When the air gap is free, a magnetic field acts on the Hall IC and the Hall voltage reaches its maximum (high). When a rotor vane obstructs the air gap, shielding the Hall IC from the magnetic flux, the Hall voltage reaches its minimum (low). The signal produced is a square wave
Hall voltage
Halo car
An automobile intended to stimulate interest in or lend prestige to an automobile line. Example: The Viper is a halo car for Dodge.
One of the chemical elements fluorine, chlorine, bromine, iodine, or astatine.

Halogenated substances
A volatile compound containing halogens, such as chlorine, fluorine or bromine.
Halogen bulb
A quartz light bulb with a tungsten filament surrounded by a trace of a halogen gas, such as iodine, bromine, fluorine, chlorine, astatine. A halogen bulb gives off a brighter light than conventional bulbs.

Halogen headlamps
Tungsten-halogen bulb used in sealed beam unit or as separate bulb in composite headlamp
Halogen headlight
High intensity reflector with inner halogen bulb, precision lens, and 3-prong attachment. Don’t touch the glass of a halogen bulb with your fingers. The oil left on the glass will cause the glass to break or reduce the life of the bulb. If the glass is accidentally touched, it may be cleaned with methylated spirits or rubbing alcohol on a soft cloth
Halogen lamp
A type of Incandescent lamp that lasts much longer and is more efficient than the common incandescent lamp. The lamp uses a halogen gas, usually iodine or bromine, that causes the evaporating tungsten to be redeposited on the filament, thus prolonging its life.
Substance containing fluorine, chlorine, bromine, and iodine.
Hamlin switch
A suspended-mass-type sensor used in new air bag systems; avoids the ecological problems associated with the earlier mercury-type switches
  1. To hit with a hammer.
  2. To ride hard and fast.
  3. Someone who rides hard and fast.
  4. Trucker slang for the accelerator pedal as in ‘When we get past this parking lot we can really hit the hammer.’
  5. A hand tool with a head (usually metal) and a handle. It is used to force one item against or through another. Several types of hammers are available
Hammer down
Trucker slang for driving fast as in ‘We got a southbound smokey with the hammer down’.
Hammer drill
Electric hand drill that hammers as well as rotates
A shaped wooden block used in panel beating, on which a desired form is produced by hammering
Hammer welding
Metalworking technique that includes gas welding, preferably without the use of filler rod, followed by hammer and Dolly work on the welded joint to smooth out any remaining imperfections
A manual which gives instructions or information.

A brake operated by a hand lever. It may also refer to the Parking brake.
Handbrake turn
180° turn achieved by applying the handbrake (acting on the rear wheels) hard when the vehicle is starting to turn
Handbrake warning light
A light on the instrument panel that illuminates when the handbrake is applied; on most new cars it has been superseded by a multifunction brake warning light
Hand controls
An auxiliary set of components to allow disabled people to operate a vehicle.
Hand Crafted
Something that is built by hand rather than in an assembly line (i.e., mass produced).
Hand crank
Before Cadillac invented and first produced electric starters, engines were started by means of a handle which was inserted into the front of the engine and rotated manually. After 1930 it became obsolete.
Hand cycle

Hand cycleHand cycle

A human powered cycle that is propelled by rotating the crank with your hands rather than your feet. Usually there is one wheel up front and two (often smaller) in the back. It is designed for people who are unable to use their legs.

Hand drill

Hand drillHand drill

A power-driven device for boring holes or (with the correct attachment) removing or securing screws and bolts

Something that is made for a specific side of a unit. For example, left hand arm rests are not interchangeable with right hand arm rests.
Hand file
A flat File for shaping metal, with a rectangular cross section, constant blade width and one smooth edge
Hand gear
Hand gear lever
A large van designed for transporting disabled people and their wheelchairs. See Invalid-carriages
Hand lapped valves
A process of grinding valves by hand so that there is a perfect match between the valve and its seat.
  1. The reaction of a vehicle under a particular circumstance, especially regarding cornering, roadholding, and maneuvering.
  2. To deal with or to cope with (e.g., ‘the tires can handle 50 psi’ means the tires can withstand pressure up to 50 psi).
  3. A CB user’s code name.
A steering device found on bicycles and motorcycles. Grips, brake levers, and shifters, etc. are attached to the handlebar.

Handlebar bag

Handlebar bagHandlebar bag

A container, usually leather and nylon, which mounts on the front of a bicycle’s handlebars.

Handlebar riser
A bracket which lifts the base of the handlebar up higher.
  1. The relative ability of a vehicle to negotiate curves and respond to road conditions. It is a factor of the weight of the vehicle, the suspension, tires, air flow, etc.
  2. The labor involved in moving product received from the trailer into the warehouse dock and then into the storage location on the ‘IN’ and moving the product out of the storage location and into a staging location to then be loaded onto a trailer on the ‘OUT’. The Warehouse Forklift / Clamp Operator moves product IN and OUT. If additional handling is involved such as opening on days off, pick packing etc., that are not the normal handling as defined in the warehouse contract, these would be defined as additional accessorial charges for handling.
  3. A single pick-up, movement and set-down of a loaded or empty pallet.
Handling Charge
Charge for normal warehouse handling (inbound or outbound, or both) to customer.
Handling Costs
Cost to warehouse or 3PL for all handling operations.
Handling system
A car cell phone that allows the driver to dial and talk on the phone without handling the phone.
A colloquial term for a passenger car with a manual transmission
Hand shield
An eye and face protector held in the hand. It enables a person to look directly at the electric arc through a special lens without being harmed.
Hand thread
Hand Truck
A non-motorized device used to transport goods manually with a pair of wheels.

Hand turn
Hand turn signal
Hang a left
To make a left-turn
Hang a right
To make a right-hand turn
Hang a U-ey
To make a U-turn
  1. A flexible ring or strap to hold a pipe, e.g., an exhaust pipe.
  2. A mounting bracket, e.g., a Spring hanger for a Leaf spring.
  3. A component of sighting point gauges, used to install the gauge at the vehicle chassis.
  4. Device attached to walls or other structure for support of pipe lines.
Hanger Bolt

Hanger boltHanger bolt

A fastener where one end is gimlet pointed and has a wood screw thread. The other end consists of a coarse machine screw thread. The center section is unthreaded.

A modification of custom cars with separate chassis, e.g., pick-ups, which raises the floorpan and lowers the body, to give the impression that the body has been pulled down over the chassis right down to street level
Hard aground
A ship which has gone aground and is not able to move under her own power.
Hard anodic coating
Hard, wear-resistant, oxide layer produced in an anodic oxidation process
Hard anodizing
A special type of anodizing adapted to the production of thick, hard, abrasion-resistant films
A board-like building material made of compressed wood chip fibers and sawdust
Hard chromium plating
An electrolytic deposition of a hard, wear-resistant, chromium layer
Hard code
A type of trouble code that causes the ECU to disengage the ABS and not re-engage it until the problem is repaired
The condition of paint when it is hard enough to polish
  1. The action of turning from a liquid to a solid.
  2. To set or to cure.
  3. The action of making the surface a metal tougher.
In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching.
Hardened pushrods
Specially treated pushrods designed for use with pushrod-guided rocker arms
Hardened Steel Nail
A heat treated and tempered steel pallet nail with a MIBANT angle between 8 and 28 degrees.
Chemical added to plastic filler to induce hardening as used in auto body repair.
  1. The process of paint, epoxy, or glue becoming hard. The drying or hardening of paint film goes through several stages. The first stage is called dust-free; at this stage, the paint has hardened sufficiently to prevent dust from becoming embedded in the paint film. The second stage is called touch-dry; at this point, the paint film can actually be touched with light finger pressure. The third and final stage is referred to as hard-dry; at this point, the paint film is hard enough to polish.
  2. A method of heat treating metals by heating to a temperature within, or above, the critical range, holding at that temperature for a given time, and then cooling rapidly, usually by quenching in oil or water.
Hardening media
A liquid into which steel is immersed in order to harden the steel. Usually involves cold water, brine, oil, and special polymers.
  1. The toughness of the surface of a metal. Normally stated in terms of Rockwell or Brinell scale of measurement, hardness shows resistance of a fastener to rough marks and abrasions, can indicate yield strength and brittleness, and has a direct relationship to tensile strength in alloy steel fasteners. However, for stainless, brass, and silicon bronze, the correlation between hardness and tensile or yield is tenuous with no definite relationship. Case-hardening uses surface heat treatment on ferrous material to cause a harder outside surface than the center. Through-hardening hardens the entire fastener. Bright hardening calls for heat treatment without oxygen, so no oxides are formed on the material surface.
  2. Resistance to plastic deformation by indentation, penetration, scratching or bending.
  3. Chain hardness is typically measured in Vickers, Brinell or Rockwell.
Hard pedal
A loss in braking efficiency so that an excessive amount of pressure is need to actuate brakes
Hard points
Specific locations, usually called out on a full-sized body draft, of points that have to be adhered to when designing surfaces. Hard points include axle centerlines, seats, pedal locations, roof and sill heights, luggage-compartment dimensions, etc.
Hard rubber


Hard shoulder
A part of the road that is divided by broken or continuous yellow lines from the rest of the road and should be used only by certain road users in certain situations
Hard-sided caravan
A British term for a trailer with foldable, hard wall panels
Hard-sided trailer
A trailer with foldable, hard wall panels
Hard solder
Uniting two pieces of metal with a material having a melting point higher than soft solder e.g., silver soldering
Hard spots
Shiny bluish/brown glazed areas on a brake drum or disc friction surface, caused by extreme heat. Excessive heat has changed their molecular structure. Hard spots can usually be removed by resurfacing
Hard stop
Hard braking, but not necessarily with locked wheels
A term for a bike (motorcycle or bicycle) which has no rear suspension
  1. A two-door or four-door vehicle without a center door post, i.e., no B-post. It gives the impression of uninterrupted glass along the side of the car. The term is derived from hardtop convertible. Other generic names have included sports coupe, hardtop coupe, or pillarless coupe. In the face of proposed rollover standards, nearly all automakers turned away from the pillarless design to a pillared version by 1976-77.
  2. A removable top made from fiberglass or steel that replaces the soft-top. It is usually painted the same color as the body of the car.
Hardtop convertible
  1. An automobile with a fixed roof that does not retract into the trunk, but gives the appearance of being a convertible because it does not have B-pillars
  2. A type of convertible having a removable hard top. Such designs include tops that unfasten and lift off such as early Ford Thunderbirds, Mercedes Retractable hardtop, and the retractable Fords of the late 1950’s.
Hardtop stand
A foldable stand that holds a detached hardtop in a vertical position when stored
Hard-top trailer

Hard-top trailerHard-top trailer

A vacation trailer with a hard top and (most often) canvas sides.

Hard trim
Instrument panel moldings, center consoles and similar plastic trim
A wood from broad-leaved species of trees (not necessarily hard or dense).
Hardy disc
A disc-style flexible coupling
Hardy-Spicer joint
A type of universal joint commonly used with prop shafts
Hardy-Spicer universal joint
A type of universal joint commonly used with prop shafts
Harley-DavidsonClick image for books on

A motorcycle manufacturer

Harmonic balancer
Also called Vibration damper. It usually is a solid crankshaft Fan belt Pulley that has a weight ring bonded by rubber to the inner crankshaft-mounted ring. The outer ring absorbs and cancels out crankshaft vibrations that otherwise might cause the crankshaft to break. Formerly, two gearwheels carrying an unbalanced weight, mounted in bearings below the middle main crankshaft bearing, driven at twice engine speed and rotating in opposite directions to counterbalance the secondary vibrations in a four-cylinder reciprocating engine.

Harmonic balance wheel
A grooved wheel attached to the front end of the crankshaft which is connected by accessory belts to the fan, alternator, power steering pump, water pump, air conditioning compressor, and other devices so that the rotating crankshaft can drive these other parts as well. The crankshaft pulley usually has timing marks located on it, and these are necessary for checking and adjusting timing with a timing light.
Harmonic Distortion
Harmonic voltage
A voltage whose frequency is a multiple of the fundamental frequency.
  1. A belt system used with child seats and in cars, consisting of two shoulder belts and two lap belt portions fastened by a central buckle.
  2. A bundle of electrical wires. For convenience in handling and for neatness, all wires going to certain part of the vehicle are bundled together into a harness. A Wiring harness.
Harness Connector
Harness ties
Self-tightening nylon straps used to bundle wires into harnesses. Once tightened, they can’t be removed unless they are cut
Harness wrap
One of several materials used to bundle wires into manageable harnesses

Harvey wallbanger
Trucker slang for a reckless driver as in ‘That 4-wheeler is a real harvey wallbanger.’
The portion of a detachable brake disc that comes in contact with the wheel hub


  1. The rear opening of a vehicle which allows passage into its cab.
  2. A hatchback.
  3. A tailgate.
  4. An opening in a deck through which cargo and stores are loaded or unloaded.


A car design in which the rear trunk and lid are replaced by a rear hatch that includes the Backlight (i.e., rear window). Usually the rear seat folds down to accommodate more luggage. Originally a hatch was a small opening in the deck of a sailing ship. The term hatch was later applied to airplane doors and to passenger cars with rear liftgates. Various models appeared in the early 1950s, but weather-tightness was a problem. The concept emerged again in the early 1970s, when fuel economy factors began to signal the trend toward compact cars. Technology had remedied the sealing difficulties. By the 1980s, most manufacturers produced one or more hatchback models, though the question of whether to call them two-door or three-door never was resolved. Their main common feature was the lack of a separate trunk. Liftback coupes may have had a different rear-end shape, but the two terms often described essentially the same vehicle.

Hatchback coupe

Hatchback coupeHatchback coupe

Originally a small opening in the deck of a sailing ship, the term hatch was later applied to airplane doors and to passenger cars with rear liftgates. Various models appeared in the early 1950s, but weather-tightness was a problem. The concept emerged again in the early 1970s, when fuel economy factors began to signal the trend toward compact cars. Technology had remedied the sealing difficulties. By the 1980s, most manufacturers produced one or more hatchback models, though the question of whether to call them two-door or three-door never was resolved. Their main common feature was the lack of a separate trunk. Liftback coupes may have had a different rear-end shape, but the two terms often described essentially the same vehicle.

Hatch battens
Flat bars which are wedged against hatch coamings to secure tarpaulin
Hatch beam
Portable beam across a hatch to support hatch covers
Hatch coaming
The vertical plating bounding a hatch for the purpose of stiffening the edges of the opening and resisting water entry
Hatch Cover
See Pontoon Hatch Cover.
Hatched marking
Chevron markings on the road which help separate traffic lanes
An opening in a deck through which cargo and stores are loaded or unloaded
Hat section
Haul Distance
Hauling snow
The loading, removing, and disposing of snow piles after snowplowing operations
Haul road
Hawse pipe
Tube through which anchor chain is led overboard from the windlass on the deck
Strong rope or steel cable used for towing, securing or mooring ships
Anything that could be a source of danger on the road

Hazard flasher switch
A switch (usually located on the steering column below the steering wheel) which makes all the signal lights flash simultaneously, to warn other vehicles that your car is disabled or going very slowly down the road. Also called 4-way warning light switch.
Hazardous location
Any area or space where combustible dust, ignitable fibers, or flammable, volatile liquids, gases, vapors or mixtures are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.
Hazardous materials
Commodities classified by the Department of Transportation as hazardous, and which require special handling and documentation. Also known as hazmat.
Hazardous material tag
A red tag attached to delivery receipts and COSOs. The tag denotes the type and amount of hazardous material in the shipment.
Hazardous wastes
Automotive wastes that are on the EPA’s list of hazardous materials or that have one or more hazardous characteristics
Hazard warning flasher
Actuates warning system of flashing front and rear turn signal lamps
Hazard warning switch
A switch (usually located on the steering column below the steering wheel) which makes all the signal lights flash simultaneously, to warn other vehicles that your car is disabled or going very slowly down the road. Also called 4-way warning light switch.
Abbreviation for Hazardous materials, as classified by the U.S. Environmental Protection Agency (EPA). Transport of hazardous materials is strictly regulated by the U.S. Department of Transportation. Also spelled HazMat
Abbreviation for hatchback.
Abbreviation for Heater Blower Voltage
Abbreviation for unburned Hydrocarbons. They are at their worst with very rich or very lean mixtures. They combine with NOx in sunlight to form Photochemical Smog.
Abbreviation for High Clutch Drum Speed
HC engine
A high-camshaft engine; the camshaft is located much higher than the crankshaft, (although not in the cylinder head), allowing for the use of shorter pushrods, thus improving the engine’s revving ability.
Abbreviation for Hydrochlorofluorocarbon. A gaseous compound that meet current environmental standards for minimizing stratospheric ozone depletion.
Abbreviation for High Compression
  1. Abbreviation for Heavy Commercial Vehicles.
  2. Abbreviation for Exhaust heat control valve
Abbreviation for Heavy duty.
  1. Abbreviation for hill descent control — A system employed on newer 4×4 vehicles which allow them to proceed down a hill more slowly so that the wheels won’t lock up.
  2. Abbreviation for Heavy Duty Cooling
Abbreviation for High-density polyethylene
Abbreviation for High Data Rate
Abbreviation for Hardtop.

Cylinder headCylinder head

  1. The upper part of something.
  2. A term used to express the increase of energy content in a fluid pumped, expressed in units of energy per unit of mass, usually simply feet.
  3. A part of the engine which covers the piston and creates the combustion chamber. The proper name is cylinder head.
  4. Pressure, usually expressed in feet of water, inches of mercury, or millimetres of mercury.
  5. The product of the water’s weight and a usable difference in elevation gives a measurement of the potential energy possessed by water.
  6. The preformed, enlarged end of a bolt, screw, pin, or rivet, provided with a bearing surface which is usually either flat or conical.
Headache rack
  1. A colloquial term for the roll bar (safety bar) above the head of the driver
  2. Heavy protective barrier mounted behind a truck tractor’s cab. Designed to prevent headaches caused by load shifting forward from the trailer and crushing the cab.
Head bolt
Head engine
  1. The action of diving or crashing into something.
  2. An exhaust manifold. The British term is headpipe.
  3. A part at the top of another part.
  4. Length of pipe or vessel, to which two or more pipe lines are joined, that carries fluid from a common source to various points of use.
  5. A shipment loaded in front of the trailer.
  6. The horizontal beam or structural member above the windshield.
Header bar
The front lateral bar of a roof which attaches to the top of the windshield frame; usually made of sheet steel shaped to match the top front edge to the curvature of the windshield
Header bow
The front lateral bar of a roof which attaches to the top of the windshield frame; usually made of sheet steel shaped to match the top front edge to the curvature of the windshield
Header panel
An exterior body panel located just ahead of the hood and surrounds the radiator.

Header point
  1. A chamfer at the end of a fastener formed at the time of heading but before threading.
  2. A chamfer point, usually of 45 degrees included angle, forming by a die at the time of heading and prior to threading.
  1. The down pipe connecting the exhaust manifold to the front of the muffler or to the connector pipe. The British term is headpipe.
  2. A special exhaust manifold that replace the stock manifold. It is designed with smooth flowing lines to prevent back pressure caused by sharp bends, rough castings, etc. Headers are frequently used in performance engine applications and are generally less restrictive than the stock exhaust manifold, resulting in increased power.
Header tank
The top radiator tank in a Thermosyphon water cooling system
Head friction
Head required to overcome friction of the interior surface of a conductor and between fluid particles in motion.
Head gasket
The seal at the top of the cylinder which sits between the cylinder block and the head. It keeps the coolant out of the combustion chamber and retains compression in the cylinder. Also called cylinder head gasket. Because it is subject to tremendous pressures, it often fails if and when an engine overheats.

Head Gasoline
Heading angle
The yaw angle.
Head key
In Britain, headlamp refers to the actual unit, whereas headlight is used for the unit as well as for its function and where emphasis is on the actual light produced by the lamp. In North America the terms are interchangeable.

Headlamp delay system
Automatically controls headlamp ON-OFF operation after ignition and main lighting switch are turned OFF
Head land
The uppermost piston Land, subject to the highest thermal load
The main light on the front of a vehicle. In Britain, headlamp refers to the actual unit, whereas headlight is used for the unit as well as for its function and where emphasis is on the actual light produced by the lamp. In North America the terms are interchangeable.

Headlight adjusting screw
A screw which moves the headlight up or down, left or right to align the beam of light
Headlight beam setting
British term for Headlight adjusting screw
Headlight body
A sheet metal pot welded or screwed to the front fender that provides the housing for the headlight and its bulbs and wiring
Headlight bucket
The headlight housing of cars or motorcycles having separate headlights not integrated into the body line
Headlight cover
  1. A rigid or flexible protection against dirt or stone damage when lights are not being used. On some vehicles, when the lights are turned on, the covers are flipped up by an electric or vacuum operated device.
  2. A clear protective cover which is permanently mounted in front of the headlights to protect the headlight itself from damage.
Headlight dimmer switch
A switch which changes the headlight from high beam to low beam or from low beam to high beam. In older vehicles, the switch was located on the floor to the far left and operated by the driver’s left foot. In newer vehicles, it is found on a stalk projecting from the steering column beneath the steering wheel. In Britain it is called the headlight dipper switch. Also called, dimmer switch.
Headlight dipper switch
British term for Headlight dimmer switch. Also called dipswitch
Headlight flasher
On some vehicles, when you flick the direction indicator lever upwards against spring pressure, the headlights flash on and off quickly. It is used to remind on-coming traffic to dim their lights or to warn them about possible hazards on the road.
Headlight leveling
A system that compensates for a heavy load in the trunk which pushes the front of the car up and causes the headlights to project upward. The leveling system levels out the projection of the light. Some will do it automatically while others have a manual control.
Headlight leveling control
Usually a manual control with a vertical thumbwheel that adjusts the height of the headlight beam
Headlight mounting panel
A sheet metal panel for rectangular headlights that is spot-welded to the front section of modern cars where the radiator grille and the headlights are mounted adjacent to each other; provides the mounting points for the headlight
Headlight on/off delay system
A system with two functions when activated, it can automatically turn ON the headlights during darkness and OFF during daylight; it can also be set to keep the headlights ON for up to approximately three minutes after leaving the parked vehicle; useful in dark, high-risk areas. The system is controlled by a photovoltaic cell on the instrument panel
Headlight retractor indicator lamp
A light on the dash that illuminates when the headlight covers are opening or closing
Headlight shell
The headlight housing of cars or motorcycles having separate headlights not integrated into the body line
Headlight visor
  1. A partial lid which encircles only the top part of the headlight.
  2. An attachment between headlight rim and lens, used only on some classic cars
Headlight wash/wipe
A system that cleans the headlights with a jet of water and a small wiper blade
Fabric or vinyl Upholstery on the interior of the roof of a vehicle and suspended by stiff, hidden wires. Late-model headliners are often molded from foam or cardboard and faced with fabric. The British term is headlining.
A British term for Headliner a soft lining on the inside of a car roof.
The bow plate on a vessel that is made of thick steel plate.
Head Marking
Raised or indented lines or dots on the top of a bolt or screw (or the side of a nut) to identify the type of material, its strength, and/or its thread type (e.g., a dot to indicate ISO metric).
Head nut
Head-on collision
An accident in which two cars hit each other’s front end. Also called head-on crash.
Head-on crash
An accident in which two cars hit each other’s front end. Also called head-on collision.
A British term for the header — the down pipe connecting the exhaust manifold to the front of the muffler or to the connector pipe.
Head pressure
  1. Pressure which exists in condensing side of refrigerating system.
  2. Force caused by the weight of a column or body of fluids. Expressed in feet, inches, or psi.
  3. Refrigerant pressure in the lines and condenser between the discharge reed valve and the expansion valve orifice
Head pressure control
Pressure-operated control which opens electrical circuit if high-side pressure becomes too high.
Head pressure safety cutout
Motor protection device wired in series with motor; will shut off the motor when excessive head pressures occur.
Head Ramp
An apparatus attached over the cab of tractors to carry motor vehicles as freight. Auto carriers may or may not have head ramps.
Another term for Head restraint
Head restraint
An extension on the upper portion of the seatback. Some are permanently attached and other are adjustable. They are designed to reduce Whiplash injuries caused by sudden stopping or collisions. They limit the rearward motion of the head and neck. Some head restraints contain radio speakers or even TV sets.

The distance between the top of a passenger’s head and the inside of the vehicle roof
Head screw
On a bicycle or motorcycle, the component that secures the forks to the frame and consists of Cups, Cones, and Ball bearings that creates the bearing mechanism that allows the fork column to rotate inside the Head tube. It thus permits the fork to turn for steering and balancing. Headsets can be either threaded or threadless.

Headset sizing
The nominal size of a headset is based on the outside diameter of the steerer. This is a source of confusion, because the steerer is not visible on an assembled bicycle. In the case of a bicycle with a traditional expander/wedge type stem, the stem shaft will be 1/8′ smaller than the steerer. Sometimes people measure the stem diameter and assume, incorrectly, that this is the size headset they have
Headset star fangled nut
A part of a threadless headset that is inserted into the fork steerer tube. The top cap bolt of a threadless headset is threaded into the star fangled nut.
Head, static
Pressure of fluid expressed in terms of height of column of the fluid, such as water or mercury.
Heads up display
(HUD) A system of mounting gauges so that the read-out is shown on the windshield. In this way the driver does not have to take his eyes off the road to see how his vehicle is performing.
Head Taper
Head tester
Head torque
Head torque wrench
Head trim
The lining of the roof.
Head tube

Head tubeHead tube

The vertical tube (visually identified as the shortest tube) in the main triangle of a bicycle frame, the one inside of which the fork column (fork steerer tube) is inserted and rotates. The Top tube and Down tube are attached to it. The fork steerer tube is inserted into the head tube.

Head velocity
Height of fluid equivalent to its velocity pressure in flowing fluid.
  1. See Austin Healey.
  2. A brand of vehicle of which the 1949-50 Silverstone models are milestone cars.
  1. That which increases the internal energy of a body by changing the motion of the molecules. This causes a change in temperature, volume, or state of the body.
  2. Form of energy which acts on substances to raise their temperature; energy associated with random motion of molecules.
  3. The energy associated with the motion of atoms or molecules in solids, which can be transmitted through solid and fluid media by Conduction, through fluid media by Convection, and through empty space by Radiation. All substances with temps above absolute zero contain heat
Heat-affected zone
That part of the base metal which has been altered by the heat from the welding, brazing, or cutting operation.
Heat balance
Heat capacity
Heat checking
Small cracks on a brake disc or drum friction surface caused by heat. Heat check can usually be removed by resurfacing
Heat checks
Cracks in the clutch pressure plate
Heat conductivity
Speed and efficiency of heat energy movement through a substance.
Heat content
The amount of heat energy available to be released by the transformation or use of a specified physical unit of an energy form (e.g., a ton of coal, a barrel of oil, a kilowatthour of electricity, a cubic foot of natural gas, or a pound of steam). The amount of heat energy is commonly expressed in Btu’s. Heat content of combustible energy forms can be expressed in terms of either gross heat content (higher or upper heating value) or net heat content (lower heating value), depending upon whether or not the available heat energy includes or excludes the energy used to vaporize water (contained in the original energy form or created during the combustion process). The Energy Information Administration typically uses gross heat content values.
Heat control
Heat control valve
Heat-control valve

Heat-control valveHeat-control valve

A valve which is controlled by temperature changes. When the ambient temperature is cold or the engine has not warmed up, it is closed so that some of the hot exhaust gases passes by the intake manifold to pre-heat the fuel mixture going to the cylinders. As the engine warms up, the valve opens up and no exhaust gases pass by the intake manifold. If the valve does not operate properly, the engine has difficulty in start up or the fuel may cause Vapor locking.

Heat cracking
A pattern of small, irregular cracks (e.g., on brake discs)
Heat crossover
A passage from one exhaust manifold up, over, and under the carburetor and on to the other manifold. Usually found on V-8 or V-6 engines. This crossover provides heat to the carburetor during engine warmup.
Heat curing adhesives
Adhesives that require a definite period of time above room temperature to develop full bond strength. They can be of one or 2 part composition. The term is usually applied to those adhesives that require 82°C or above to effect a cure
Heat dam
A thin groove cut into the head of a piston between the top ring groove and the top of the piston. The heat, instead of passing through the aluminum of the piston to the ring, encounters the heat dam. This helps to minimize heat transfer.
Heat dissipation
The transfer of heat. In brake systems the heat produced by braking is transferred to the air.
Heated air inlet system
(HAI) a system that operates during cold weather and cold start. Brings warm, filtered air into the engine to control the volume of air entering the engine, vaporize the fuel better and reduce HC and CO emissions
Heated exhaust gas oxygen sensor
(HEGO) an EGO detection device with a heating element
Heated intake
A device that helps to Vaporize the gasoline in a cold engine. The Thermostat in the air cleaner horn is connected to the outside of the exhaust manifold. When the engine is cold, the Thermostat closes a Damper in the Air cleaner horn so that air going to the carburetor does not come through the open end of the horn. Instead the air comes from above the hot exhaust manifold. As the engine warms up, the Thermostat opens the damper so that air is taken in from the end of the horn.
Heated oxygen sensor
An oxygen detection device (O2S) which is heated to improve sensor performance
Heated rear window
A rear window with a heating element that Defogs (Demists) inside and Defrosts (De-ices) the outside either by fine wires embedded or etched in the glass or by a heater and fan.
Heated tool welding
A welding process in which the parts to be welded are pressed against a heated plate and subsequently pressed together to produce a fusion weld
Heated windshield
Windshield with a heating element to facilitate defrosting (de-icing)
A device which gives off heat. In automobiles, it heats the interior of the vehicle. In a water-cooled engine the coolant is channeled through the heater in the passenger compartment. Some cars used an electric or gasoline heater because they had no engine coolant (e.g., the Volkswagen Beetle).

Heater air pipe
A channel section incorporated into the side member or other structural sections that is designed to provide a flow of warm air into the interior of the vehicle, above all into the footwells (e.g., as used on the VW Beetle)
Heater blower
Electric fan to boost heating and ventilation. Also called heater fan
Heater core
A finned unit located in the passenger compartment and through which coolant from the engine flows to heat the unit. A fan blows air over the unit to heat the passenger compartment
Heater fan
Electric fan to boost heating and ventilation. Also called heater blower
Heater flange
Heating element for preheating the intake air in small diesel engines
Heater plug


Heater-plug indicator
Heater system
Heater-ventilation system
The system in a vehicle interior that provides heat or fresh air or both.
Heat exchanger
A device which transfers the heat of one substance to another (i.e., from a warm or hot surface to a cold or cooler one) such as evaporators, condensers, and radiators.
Heat fade
Temporary reduction of brake effectiveness due to a loss of friction between braking surfaces, resulting from heat
Heat index
A number representing the effect of temperature and humidity on humans by combining the two variables into an apparent temperature. Introduced as a replacement for the temperature-humidity index. Later replaced by the Canadian introduced Humidex
Heating And Cooling
Heating coil
Heat transfer device consisting of a coil of piping, which releases heat.
Heating control
Device which controls temperature of a heat transfer unit which releases heat.
Heating element
All parts which transmit heat from flames or flue gases to the medium being heated and in contact with both.

Heating equipment
Any equipment designed and/or specifically used for heating ambient air in an enclosed space. Common types of heating equipment include: central warm air furnace, heat pump, plug-in or built-in room heater, boiler for steam or hot water heating system, heating stove, and fireplace. Note: A cooking stove in a housing unit is sometimes reported as heating equipment, even though it was built for preparing food.
Heating System
Heating value
Amount of heat which may be obtained by burning a fuel. The heating value is usually expressed in BTU per lb., BTU per gal., or kJ/kg.

Heat intensity
Heat concentration in a substance as indicated by the temperature of the substance through use of a thermometer.
Heat lag
The time it takes for heat to travel through a substance heated on one side.
Heat leakage
Flow of heat through a substance.
Heat load
Amount of heat, measured in BTU or watts, which is removed during a period of 24 hours.
Heat loss
Heat from burning fuel that is lost in the cylinder without doing useful work.
Heat of Combustion
Heat of compression
Mechanical energy of pressure changed into energy of heat.
Heat of condensation
The heat liberated by a unit mass of gas at its boiling point as it condenses to a liquid. Equal to the heat of vaporization

Heat Of Evaporation
Heat of fusion
Heat released from a substance to change it from a liquid state to a solid state. The heat of fusion of ice is 144 BTU per pound (335 kJ/kg).
Heat of respiration
Process by which oxygen and carbohydrates are assimilated by a substance; also when carbon dioxide and water are given off by a substance.
Heat of vaporization
The heat absorbed per unit mass of a given material at its boiling point that completely converts the material to a gas at the same temp. Equal to heat of condensation

Heat path
The path along which heat passes from the spark plug tip to the water jacket
Heat pipe, gas forced-air
High efficiency gas furnace that uses vertical liquid filled pipes. The pipes are heated by a burner at their base, and the liquid boils and vaporizes within the pipe. The furnace blower circulates air over the pipes for heating.

Heat pump
Compression cycle system used to supply heat to a temperature-controlled space. Same system can also remove heat from the same space.
Heat quantity


Heat range
Refers to the operating temperature of a given style of spark plug. Plugs are made to operate at different temperatures depending upon the thickness and length of the Porcelain insulator as measured from the sealing ring down to the tip. In this way it transfers heat from the combustion chamber to the cylinder head. The speed at which it transfers heat is considered in terms of hot and cold plugs. A hot plug transfers heat slowly, causing the plug to operate at a higher temperature. A cold plug transfers heat more quickly, thus operating at a lower temperature. If a plug is too cold, it will foul. If it is too hot, it will cause Preignition.

Heat range reserve
The distance to the start of pre-ignition under further increasing thermal loading of the spark plug. This reserve is expressed in degrees crankshaft, the amount by which the factory-set ignition timing can be further advanced without preignition occurring
Heat reactivate
To soften a dried thermoplastic adhesive film to a sticky state by application of heat. Used as a method of bond
Heat reactivation
To restore the tackiness of the adhesive with heat, and then to bond under pressure
Heat recovery system
Produces and stores hot water by transferring heat from condenser to cooler water.
Heat riser
  1. An area, surrounding a portion of the intake manifold, through which exhaust gases can pass to heat the fuel mixture during warmup.
  2. The flapper in the exhaust manifold that is closed when the engine is cold, causing hot exhaust gases to heat the inlet manifold, thus providing better cold engine operation; a thermostatic spring opens the flapper when the engine warms up
Heat Sensor
Heat shield
A sheet metal part, usually reflective, often asbestos-lined. It protects heat-sensitive components from heat Radiation of the exhaust system. Also called heat shroud.

Heat shrinking
Shrinking dents in panels using a gas welder to heat local areas of the dents
Heat shrink tube
A thin, rubber-like hose into which bare electrical wire is inserted. When the tube is heated, it shrinks to fit the wire, thus protecting the wire from touching other wires, etc.
Heat-shrink tubing
Plastic tube used to insulate electrical solder joints.
Heat shroud
Heat sink
  1. Heat removing/dissipating component, such as the fins on an air-cooled cylinder
  2. Relatively cold surface capable of absorbing heat.
Heat soak
Heat from the engine warming the carburetor and other parts of the fuel system which can cause vapor lock and may make restarting difficult
Heat transfer
  1. The transfer of thermal energy from one material to another by means of thermal Conduction, Convection, or Radiation; heat transfer is possible only from a high to a low temperature level
  2. Movement of heat from one body or substance to another. Heat may be transferred by Radiation, Conduction, Convection, or a combination of these three methods.
Heat transfer module
Primary system of heat transfer in a glycol water solution forced-air furnace. The heat transfer module contains the ignitor, burner, and primary solution circulating coil.
Heat transmission
The flow of heat from one substance to another
Heat Treating
An operation involving the heating and cooling of a metal to obtain certain desirable conditions or properties.
Heat treatment
A combination of heating and cooling operations timed and applied to a metal in a solid state in a way that will produce desired properties especially to strengthen and harden it.
Heat value
Heat content of the fuel in Btu’s per pound or gallon.
Heavy braking
The action of applying the brakes fast and hard especially during an emergency stop. Opposite to Light braking
Heavy cable
Cable that is used for severe service where high strength is required. Opposite to Light cable
Heavy clutch
Having a stiff operation, e.g., requiring considerable effort to push down the pedal on cars and trucks; or squeeze the lever on motorcycles. Opposite to Light clutch
Heavy crude
Crude oil with a high specific gravity and a low API gravity due to the presence of a high proportion of heavy hydrocarbon fractions and metallic content.
(HD) Something that is built for heavy loads or severe use. Opposite to Light-duty
Heavy-duty diagonal cutting pliers
Diagonal cutting pliers with a special joint and handle design for extra cutting power
Heavy-duty end cutting pliers
End cutting pliers with a special joint and handle design for extra cutting power
Heavy-duty ring wrench
A strong single end box wrench for use with a tubular handle. It can be used without the handle for quickly spinning on nuts or, with the handle slipped on, for final tightening or reaching otherwise inaccessible nuts
Heavy-duty truck
Vehicle weighing from 26,001 to 33,001 lbs. Also included off-highway trucks.

Heavy-duty wrench
A tool which can withstand severe use (and abuse) before breaking
Heavy film build
Excessive thickness of paint coating
Heavy foot
To drive at full throttle or high speeds as though the driver’s foot were very heavy so that the natural pressure of the foot against the throttle pedal caused high speeds
Heavy gas oil
Petroleum distillates with an approximate boiling range from 343.9°C to 537.8°C.
Heavy goods vehicle
(HGV) A British term expressing a vehicle capable of carrying heavy loads and requiring a special license to drive HGV.
Heavy machinery cargo
This category of cargo will tend to be on flatbed trucks and trailers. Examples: Off road-vehicles, like bulldozers and backhoes, forklifts, construction machinery, large lathes, and farm tractors.
Heavy metals
Metallic elements, including those required for plant and animal nutrition, in trace concentration but which become toxic at higher concentrations. Examples are mercury, chromium, cadmium, and lead.
Heavy oil
The fuel oils remaining after the lighter oils have been distilled off during the refining process. Except for start-up and flame stabilization, virtually all petroleum used in steam plants is heavy oil. Includes fuel oil numbers 4, 5, and 6; crude; and topped crude.
Heavy paint
Thickly coated. Opposite of Light paint
Heavy phosphating
Application of extremely heavy phosphate coatings
Heavy rail
An electric railway with the capacity for a heavy volume of traffic and characterized by exclusive rights-of-way, multi-car trains, high speed and rapid acceleration, sophisticated signaling, and high platform loading. Also known as subway, elevated (railway), metropolitan railway (metro).
Heavy sheet metal
Thick sheet metal for severe use beyond the average. Opposite of Light sheet metal
Heavy side pattern
An oval spray pattern that is thicker toward the left or right hand side, i.e., it takes the shape of a crescent oriented towards the right or left. This is often caused by a clogged horn hole at the air cap of the spray gun
Heavy steering
Having a stiff operation, e.g., requiring considerable effort to turn the steering wheel. Opposite of Light steering
Heavy traffic
A road with a lot of moving vehicles. Opposite of Light traffic
Heavy water
Water containing a significantly greater proportion of heavy hydrogen (deuterium) atoms to ordinary hydrogen atoms than is found in ordinary (light) water. Heavy water is used as a moderator in some reactors because it slows neutrons effectively and also has a low cross section for absorption of neutrons.
Heavy yellow boot
A Denver boot
  1. The end of the brake shoe which rests against the Anchor pin.
  2. The end of the brake shoe furthest from where the braking force is applied.
  3. The wide end of a tapered gear tooth such as found in the Differential gears.


  4. The rubbing block on the contact breaker lever.
  5. A bead heel.
  6. To lean to one side so that the centerline plane of a vehicle or ship is not vertical. Also called list.
Heel and toe
A driving technique where the driver places the left side or the toes of his right foot on the brake pedal and the right side or the heel of his right foot on the throttle pedal so that he can simultaneously brake and blip the throttle for a downshift. This is done to lessen the strain on the Gearbox and Drivetrain and makes for smoother driving.
Heel and toe wear
Uneven wear of tread blocks on a tire. The trailing edge of the block often tends to wear at a faster rate that the leading edge.
The vertical transverse sheet metal panel running across the width of the car interior at the front edge of the rear seat well; this panel links the rear seat well to the floorpan and provides rigidity for both panels. Also called heel plate. Compare Toeboard
Heel dolly

Heel dollyHeel dolly

A Dolly in the form of a heel of a foot or shoe to shape and straighten dented panels, usually by holding the dolly behind the metal to be shaped and hammering the metal.

The inclination of a vessel to one side.
Heel plate
The vertical transverse sheet metal panel running across the width of the car interior at the front edge of the rear seat well; this panel links the rear seat well to the floorpan and provides rigidity for both panels. Also called heelboard. Compare Toeboard
Abbreviation for heated exhaust gas oxygen.
HEGO sensor
A device which detects heated exhaust gas oxygen.
Abbreviation for High energy ignition
Abbreviation for High energy ignition system with electronic spark timing
Height adjustable steering column
A steering column which can be lengthened or shortened to suit the individual driver
Height corrector
An automatic leveling control in hydropneumatic suspension systems
Height hamper pitch control


Height of Thread
The distance, measured perpendicular to the axis, between the major and minor cylinders or cones, respectively.
Height regulator
An automatic leveling control in hydropneumatic suspension systems
Heim joint
An extremely rigid articulating Joint, commonly known as a spherical rod-end, used in any precision linkage. Heim joints are often used in the suspension links of race cars because they locate wheels very precisely.
A spiraling shape such as that made by a Coil spring. In the shape of a helix.

Helical differential
Virtually all gears in modern cars are cut with a spiral helix angle rather than straight meshing. Straight gears are simpler to manufacture, but are extremely noisy.
Helical gear

Helical gearHelical gear

A gear that has the teeth cut at an angle to the center line of the gear. This kind of gear is useful because there is no chance of intermittent tooth-to-tooth operation because there are at least two teeth engaged at any time. Also helical gears tend to operate quieter than straight-cut gears, but they do absorb a slight amount of power due to side thrust.

Helical Nail
A helically (continuous spiral) threaded pallet nail, see also drive screw nail.
Helical spring lock washer
A locking device for threaded fasteners
Helical teeth
Curved gear teeth on the edge of a gearwheel, cut at an angle to its axis
  1. A trade name for a coil-type thread insert, commonly used to replace a stripped spark plug thread.
  2. Coil of wire used as an insert to accept a screw or bolt and adding holding power by forcing itself between the fastener and the walls of the recess when the fastener is driven in.
A mirror that reflects solar rays onto a central receiver. A heliostat automatically adjusts its position to track daily or seasonal changes in the sun’s position. The arrangement of heliostats around a central receiver is also called a solar collector field.
Helium leak test
A pressure test using helium
A spiral, like the thread on a screw or a coil spring in a suspension system
Steering wheel installed on the bridge or wheelhouse of a ship to turn the rudder during maneuvering and navigation
  1. A protective device for the head of bicycle and motorcycle riders as well as race car drivers.
  2. A protecting hood which fits over the arc welder’s head, provided with a lens of safety glass through which the operator may safely observe the electric arc.
Helmet connector
A special type of lug for connecting a battery with tapered terminal posts. Also called helmet lug.
Helmet hair
The condition of a person’s hair after wearing a helmet for a period of time. Short hair tends to stand on end while long hair tangles and/or becomes flat.
Helmet lug
A special type of lug for connecting a battery with tapered terminal posts. Also called helmet connector.
Helmhotz free energy
(A or F in US) Similar to Gibbs free energy but with internal energy substituted for enthalpy. A negative change in A is indicative of a spontaneous change in a closed system at constant volume.
Helper leaf
An additional spring device (usually another Leaf spring) which permits a greater load on the axle. Also called helper leaf.
Helper spring
An additional spring device (usually another Leaf spring) which permits a greater load on the axle. Also called helper leaf.
Engine using Hemispherical-shaped (half of a globe or sphere) combustion chambers. The valves are cocked at 45 degrees from the piston top. Mopars, despite their fame, are not the only cars with hemi heads.

Hemi head


Hemispherical combustion chamber

Hemispherical Combustion ChamberClick image to supersize

A round, dome-shaped combustion chamber. This shape permits larger valves and straighter Intake and exhaust ports for improved Breathing. Its small surface area in comparison to volume reduces the amount of heat loss. It is used in high performance cars and racing engines.

(H) A unit of inductance, equal to the inductance of a circuit in which the variation of current at the rate of one ampere per second induces an electromotive force of one volt. The term was named after US physicist, J. Henry (1797-1878)
Hermetic compressor
  1. Compressor in which the driving motor is sealed in the same dome or housing as the compressor.
  2. Compressor which has the driving motor sealed inside the compressor housing. The motor operates in an atmosphere of the refrigerant.
Hermetic motor
Compressor drive motor sealed within same casing which contains compressor.
Hermetic system
Refrigeration system which has a compressor driven by a motor contained in compressor dome or housing.
Herringbone gear
Herringbone gears
Two Helical gears operating together and so placed that the angle of the teeth form a V shape.

Herringbone pattern
The characteristic pattern cut by a tool bit when a brake drum is machined without the proper use of a dampening belt.
(hz) Correct terminology for cycles per second.
The term used to describe a problem in Driveability. The engine momentarily fails to respond to a push on the accelerator. The cause is usually a lean fuel-air mixture (i.e., more air than fuel) or retarded timing.
Abbreviation for Hydraulic-Electronic Unit Injector
Abbreviation for Hybrid-Electric Vehicle
A recessed six-sided socket in the head of a cap or set screw to add greater tightening and loosening power. Used with a hex key wrench.
Hexagonal bolster
A tool that allows a screwdriver to be turned with a wrench for extra torque to loosen tight screws
Hexagonal collar
A tool that allows a screwdriver to be turned with a wrench for extra torque to loosen tight screws
Hexagon bit
A screwdriver bit with six sides
Hexagon bolt
A fastener with a six-sided head

Hexagon Head
Flat top surface with six sides and with a flat bearing surface.
Hexagon key
A key for hexagon recess screws, 90° offset at one end. Also called an Allen key
Hexagon screwdriver
Hexagon socket
Hex bit
A screwdriver bit with six sides
Hex bolt
A bolt with a six-sided head
Hex head cap screw

Hex boltHex head cap screw

A bolt with a six-sided head that must be installed or removed with an appropriately sized wrench.

Hex key
A key for hexagon recess screws, 90° offset at one end. Also called an Allen key
Hex wrench
An L-shaped tool that works like a screwdriver, designed to remove screws with hexagonal holes in their heads.

  1. Abbreviation for Hydrofluorocarbon
  2. Abbreviation for Highspeed Fan Control
Abbreviation for High Fuel Pump (Relay) Control
Abbreviation for heated front seat as found in advertisements
Chemical symbol for mercury. Used when referring to vacuum as inches of mercury. Heavy silver-white metallic element; only metal that is liquid at ordinary room temperature.
Abbreviation for Heavy goods vehicle (over 1.5 tons)
Chevrolet HHR BooksClick image for books on
Chevrolet HHR

A model of small van-like car produced by the Chevrolet division of General Motorsfrom 2006 in answer to Chrysler’s PT Cruiser

Abbreviation for Higher heating value
Abbreviation for Hot-Idle Compensator (Ford)
Abbreviation for High-intensity discharge
Hidden wiper
A wiper system with a parking position below the normal visibility range
Hide-away headlights
Hideaway wiper
A wiper system with a parking position below the normal visibility range
The ability of a paint to obscure the surface to which it is applied.
HIF carburetor
Type of SU carburetor with a horizontal integral float chamber
High and tight
Loading freight high in a trailer uses the full cube of the trailer and allows more freight to be loaded. Loading freight tight in a trailer eliminates the possibility of damage while en route.
A term used in car sales, the practice of stating a very high trade-in price to a customer who is known or expected to be shopping around, comparing prices. When the customer finds that other dealers cannot match the trade-in price, he will return to the original dealer, only to be told that the inflated figure was a mistake (e.g., based on wrong assumptions as to the trade-in’s clutch condition, etc.). Many customers will then accept a new, lower price because they are tired of shopping around.


High beam
All cars have at least two levels of lighting for night driving. The Low beam is used when there are other vehicles approaching or when you are following another vehicle. The high beam is used when driving on poorly lit roads where there is no visible traffic. The high beam light may be an integral part of the headlight assembly or is the inboard light when there are two Lamps on each side of the vehicle. When the lamps are stacked vertically, the high beam is the upper one. When the high beam switch is activated, the low beam lights may or may not be switched off. In a system with factory installed day-time running lights, the high beam light is illuminated at a lower intensity. The British term for high beam is main beam.
High beam indicator
A blue light on the instrument panel which comes on when the high beams are activated. Also called beam indicator. The British term is main beam indicator.
High box
Status of the transmission when the two-speed transfer gearbox lever is in the high ratio position –for normal, on-road, day-to-day use.
High-build filler
A spray primer that leaves a relatively thick coat on the panel surface to cover up minor imperfections that would otherwise show up very prominently in the final color coat
High-build galvanizing
A galvanizing process in which extremely heavy zinc coatings are applied
High-camshaft engine


High carbon steel
A very hard steel, as opposed to plain carbon steel. Hypereutectoid steels containing more than 0.8% carbon. Such steels consist of iron carbide (cementite) and pearlite when slow cooled. They are capable of being heat treated to high hardness, but tend to be brittle. Used for metal working formers and fine edge cutting tools (e.g., files)
Vehicle is stationary because the driving wheels are no longer touching the ground.
High center rim
A raised center rim design, used in the Cts wheel
High compression head
A cylinder head with a smaller combustion chamber area thereby raising the compression. The head can be Custom built or can be a stock head Milled (cut) down.
High Crown Dolly
A curved block of cast iron for shaping high crown radius panels with a bumping hammer. It has a rounded corner which is useful for bringing up low spots as is done with a pick hammer
High crown panel
A panel shape that curves rapidly in all directions, e.g., around the headlights of older cars. The opposite is Low crown panel
High crown spoon
A spoon with a broad working surface and a heavily rounded tip that is ideal for using as a Dolly or a lever in confined areas, such as headlight housings or rounded body sections above the waistline
High-density polyethylene
(HDPE) A very tough, chemically resistant thermoplastic, with a soapy touch; e.g., used for blow-molded parts such as fuel tanks or other moldings, such as bumpers
High efficiency gas furnace
Furnace which uses recycling of combustion gases or pulse combustion to obtain operating efficiencies from 85 to 95 percent.
High efficiency lighting
Lighting provided by HID lamps and/or fluorescent lamps.
High energy battery
An innovative battery type developed for electric cars
High energy coil
A coil which generates higher ignition voltage and/or offers increased spark efficiency; ballasted
High energy ignition
(HEI) an electronic ignition system used by GM
High energy ignition system
(HEI) An ignition system which provides more ignition power (higher voltage at higher amperage) than normal systems; a typical HEI includes an electronic control unit and magnetic pick-up in combination with mechanical ignition timing
High energy ignition system with electronic spark timing
(HEI-EST) A system consists of an electronic distributor, with the ignition coil mounted on the distributor cap on 6- and 8-cylinder models or externally on 4-cylinder models; the ignition timing is performed electronically by the electronic control module. (Used on several GM models since 1983.)
Higher Heating value
(HHV) The value of the heat of combustion of a fuel as measured by reducing all of the products of combustion back to their original temperature and condensing all water vapor formed by combustion. This value takes into account the heat of vaporization of water.
Higher-Learning In Alternative Motorfuels Program
High gear
The top gear or the cruising gear of a transmission. It is usually the highest number, i.e., fifth gear of a Five-speed transmission.
  1. A transmission (even like the chain system on a bicycle) where a large gear drives a small one. The larger the drive gear and the smaller the driven gear the higher the gear ratio. It will result in high speed, but is poor for getting started from a stop.
  2. A vehicle’s transmission system which has a higher than usual gearing, to improve fuel economy.
High gear pinion
Top gear on the mainshaft in a direct drive transmission. All gear ratios drive through the high gear pinion, which also holds the output sprocket.
High gloss
Very shiny, bright appearance
High Impedance Injectors
Fuel injectors designed to work with a simple switch in a 12 volt circuit, no special signal conditioning is required to drive them. The resistance of a high impedance injector is about 10-15 ohms. Also called hi-Z
High impedance voltmeter
A voltmeter with high opposition to the flow of electrical current. Good for reading circuits with low current flow, such as found in the CCC system
High-intensity discharge
(HID) A lamp that produces light by passing electricity through gas, which causes the gas to glow. Examples of HID lamps are mercury vapor lamps, metal halide lamps, and high-pressure sodium lamps. HID lamps have extremely long life and emit far more lumens per fixture than do fluorescent lights.
High-intensity discharge lamp
A lamp that produces light by passing electricity through gas, which causes the gas to glow. Examples of HID lamps are mercury vapor lamps, metal halide lamps, and high-pressure sodium lamps. HID lamps have extremely long life and emit far more lumens per fixture than do fluorescent lights.
High lead screw
A screw with a low pitch so that an engaged nut would move an appreciable distance with a partial revolution.
High leverage diagonal cutting pliers
Diagonal cutting pliers with special joint and handle design for extra cutting power
High leverage end cutting pliers
End cutting pliers with special joint and handle design for extra cutting power
High lift rocker arm
High lift rocker arms
Custom Rocker arms designed so that a standard lift of the Push rod will depress or open the valve somewhat more than the stock Lifter.
Light that bounces noticeably off a peak or line or convex surface.
High load condition
Occurs when the air conditioner system must operate continuously at maximum capacity to supply enough cold air
High-Low Firing combustion controls
The action of a combustion control which positions the air and fuel supply for low-fire and for high-fire in accordance with load demand.
High/low range gearbox
High/low range transmission
High-Mileage Vehicle
A vehicle that exceeds 12,500 miles (20,000 km) per year. For example, a four-year old car has high miles if the odometer reads more than (12,500 x 4) 50,000 miles (80,000 km).
High-mileage households
Households with estimated aggregate annual vehicle mileage that exceeds 12,500 miles (20,000 km).
High-mounted brake light
Third brake light mounted in the middle of the rear window or on some cars integrated in the trailing edge of the rear deck spoiler
High Occupancy Vehicle
(HOV) Vehicles having more than one occupant. Examples include carpools, vanpools, buses, and mini-buses. Transportation systems may encourage HOV use by having designated HOV lanes.
High Occupancy Vehicle Lane
(HOV Lane) Exclusive road or traffic lane limited to buses, vanpools, carpools, emergency vehicles, and in some cases, single occupant motorcycles. HOV lanes typically have higher operating speeds and lower traffic volumes than adjacent general purpose lanes. HOV lanes have proven to be successful in major metropolitan areas across the US; however, their full effectiveness is usually not realized until about one to two years after implementation.
Producing better than average results
High-performance header
A special exhaust manifold, which is not made of cast iron as usual, but of specially designed, curved and welded steel tubes, to produce a smooth flow path for the exhaust gases, avoiding any sharp bends; less heavy, less sturdy and more expensive than an ordinary manifold; usually replaces the down pipe
High Platform Bus
Depicting heavy-duty, OTR coaches and tour buses designed for long-distance or intercity travel. Passenger platform higher than driver’s seat, with large cargo holds under floor. May have a washroom. Some are two axle vehicles but most are found with three axles: One steering, one four-wheeled drive and one two-wheeled tag axle.
High pressure
Operating under a lot of pressure e.g., braking systems or diesel fuel injection
High-pressure boiler
Boiler furnishing steam at pressures of 205 kPa gauge or higher.
High-pressure cut-out
Electrical control switch operated by the high-side pressure which automatically opens electrical circuit if too high pressure is reached.
High pressure foaming
A process in which plastics are foamed under high pressure (6-50 Bar). The opposite is Low-pressure foaming
High-pressure gauge
Instrument for measuring pressures in range of 0 psia to 500 psia (101.3 kPa to 3600 kPa).
High pressure line
The line(s) carrying high pressure liquid and gas from the compressor outlet to the expansion valve inlet
High pressure relief valve
  1. A safety valve located in the discharge line (six-cylinder compressors) or the compressor block (two-cylinder compressors)
  2. Located somewhere on the high side of the air conditioning system often next to the receiver drier this safety valve protects the system against excessive pressure
High ratio
A condition of the transmission when the transfer gearbox lever is in the high position.
High revs
Towards the top end of the scale of engine revolutions
Highrise manifold
High-rise manifold
An intake manifold designed to mount the carburetor or carburetors, considerably higher above the engine than is done in the standard manifold. This is done to improve the angle at which the fuel is delivered.
High side
  1. In air conditioning systems, the high side (i.e., high pressure side or discharge side) is located between the compressor and expansion valve or orifice tube and includes the condenser. The opposite is Low side
  2. Parts of a refrigerating system which are under condensing or high-side pressure.
  3. Another term for discharge side. The part of the air conditioning system under high pressure, extending from the compressor outlet to the thermostatic expansion valve/tube inlet
High-side float
Refrigerant control mechanism which controls the level of the liquid refrigerant in the high-pressure side of mechanism.
High-side float flooded system
Refrigeration system which has a float operated by the level of the high-side liquid refrigerant.
High-side service valve
A device, located on the discharge or high side of the compressor, at which high side pressure can be checked and other service operations can be performed
High side service valve
A device, located on the discharge or high side of the compressor, at which high side pressure can be checked and other service operations can be performed
High siding
Pitching a bike over away from the direction you are turning. The most dangerous kind of crash
High-speed bleeds
Main air bleeds; located in the air horn
High-speed circuit
Main metering system
High speed direct injection
(HSDI) A system for rapid injection of fuel into a diesel engine
High spot
A raised area on a panel surface
High-temperature collector
A solar thermal collector designed to operate at a temperature of 82°C or higher.
High temperature superconductivity
A phenomenon discovered by Karl Alex Müller and Johannes Georg Bednorz of IBM-Zurich in 1987 in which a compound containing copper, oxygen, barium, and lanthanum exhibited superconductivity at temperatures as high as 35°K. Subsequently in 1987, C. W. Paul Chu and Maw-Kuen Wu at the Universities of Houston and of Alabama-Huntsville respectively, developed a compound which was superconducting at temperatures as high as 90°K, a temperature above that of liquid nitrogen, a low cost substance. Several other compounds have been found to yield similar results. A number of theories have been proposed to explain this phenomenon. See Meissner effect.
(HT) capable of operating at a relatively high voltage
High-tension battery
A UK term for a B-battery
High-tension circuit
High-tension distributor
A distributor, in electronically controlled ignition systems, which has no controlling functions or advance mechanism
High tension lead
High voltage wire from the ignition coil. May also indicate the Secondary wire from the ignition coil to the distributor and wires from the distributor to the spark plugs.
High tension leads
High-tension leads
The wire which goes from the ignition coil to the distributor and the wires which go from the distributor to each of the spark plugs.

High-tension winding
High test
Premium gasoline with the highest octane rating
High-vacuum pump
Mechanism which can create a vacuum in the 1000 to 1 micron range.
High-voltage distribution
High-Voltage Electric Circuit
A circuit operating at more than 600 volts nominal.
High-voltage reserve
The difference between the available ignition voltage and the ignition voltage required at a given moment
Any public road outside the cities with a foundation and a hard surface. Originally, the highway was a way higher than the ground, e.g., as opposed to stage coach tracks. Since similar speed limits exist in the USA and Canada for all types of highways, both single or multilane (usually between 50 and 70 mph or 80 and 110 kph), the terms highway driving speeds and highway driving should not be associated with speeds higher than 70 mph (110 kph).

Highway bar
An auxiliary lateral piece of metal (usually chromed for good appearance) fitted to the front down tubes or frame. Folding Pegs may be found at each end. The bar allows the rider to position his feet straight ahead for variety in leg position when riding long distances. Also called hi-way bar.
Highway Code
Official British code of conduct for all road users
Highway marker shield

Interstate shieldInterstate shield

A road sign which indicates the type and road number of a highway. In some cases the direction of travel (nearly always North, South, East or West) is also indicated.

Highway peg
A folding footrest which is mounted on the ends of a Highway bar
Highway Safety
Highway Tractor
The truck portion of semi-tractor-trailer unit or train which is designed to pull a semitrailer by means of a fifth wheel mounted over the rear axle(s). Also called a Truck tractor
Highway Traffic Safety Administration
Hi-lift jack
Versatile lever-operated mechanical bumper jack capable of a lift of a metre or more.
Hill descent control
(HDC) A system employed on newer 4×4 vehicles which allow them to proceed down a hill more slowly so that the wheels won’t lock up.
Hill holder
A mechanically or electromechanically engaged device for preventing accidental rearward movement of a vehicle prior to driving away; found mainly in automatic transmissions
Hill-holder system
A system that locks the brakes in the applied position on uphill grades when the driver’s foot is removed from the brake pedal.
HillmanClick image for books on

A model of automobile manufactured in England

Hi-lo lever
Term sometimes used to describe the transfer gearbox lever. High Load suspension. An option on the Defender 90 enabling payload to be raised by about 150 kg.
A brand name fork lift. Also refers to the ability of the truck to lift and put down freight.
Hinge bow


Hinged-caliper disc brake
An old disc brake design formerly used on motor cycles; superseded by sliding-caliper disc brakes
Hinged quarter window
A rear side window between the B-post and the C-post and/or in the case of station wagons, between the C-post and the D-post. It is provided with hinges to allow it to be opened
Hinge facing
A part of the door frame that includes the bracing and threaded plate for mounting the hinge to the door. It is not to be confused with the Hinge panel that is part of the hinge pillar of the body shell.
Hinge panel
Sheet metal panel spot-welded to the A-post or rear of the front fender that accommodates the hinges for the front door
Hinge pillar
The vertical structural post to which the vehicle doors are attached. In most instances, the front doors are attached to the A-pillar while the rear doors are attached to the B-pillar. In a vehicle with suicide doors, the front doors are attached to the B-pillar while the rear doors (if suicide type) is attached to the C-pillar.
Hinge pillar reinforcement
The vertical section behind the visible A-pillar
Hinge plate
The reinforcing plate between the hinge and the door panel which distributes the forces acting on the hinge bolts over a larger area of the panel
Hinge post
Hinge tapping plate
The threaded plate housed in a sheet metal cage spot-welded to the hinge pillar or, in some cases, to the door frame; the door is bolted to this plate and may be adjusted within certain limits, as the plate can be moved about in its sheet metal cage
Hip belt


Hi perf
Abbreviation for high performance, also called hi-po or hi po.


Hispano Suiza
A brand of vehicle of which the H6 from 1919, all French models, and the Spanish models T56, T56BIS, T64 are classic cars.
a truck or automobile with special wheels that drop down on the railroad track and allow it to drive on railroads as well as on highways.
  1. To connect or couple up a motorhome or trailer to a towing vehicle.
  2. The bracket used to connect a vehicle to a trailer or motorhome.
Hitch class II

Hitch class IIHitch class II

A trailer hitch rated at 3500 lb gross trailer weight and 350 lb tongue weight.

Hitch ball

Hitch ballHitch ball

A metal ball with a bolt attached to it. It is secured to a bracket on a vehicle in order to mount a trailer hitch. British term is towball

Hitch pin
A heat-treated, hi-strength steel pin ranging from a diameter of 7/16′ to 1-1/4′ and a length from 3-1/2′ to 7′. A flange is at one end and a hole (through which a Hair pin cotter or Hitch pin clip can be inserted) at the other end. The hitch pin secures the hitch to the receiver.

Hitch pin clip

Hitch pin clipHitch pin clip

A Hair pin cotter with one straight leg. Insert the straight leg into the hole of a rod so that the bent leg will encircle the rod.

Hitch rack
A bicycle rack mounted to the hitch on the rear of a car or truck. Available in ball mount, 1.25′ receiver, and 2′ receiver versions.
Premium gasoline with the highest octane rating
Hi-way bar
An auxiliary lateral piece of metal (usually chromed for good appearance) fitted to the front down tubes or frame. Folding pegs may be found at each end. The bar allows the rider to position his feet straight ahead for variety in leg position when riding long distances. Also called highway bar.
Abbreviation for High Impedance Injectors


Abbreviation for Hardware Limited Operation System

Abbreviation for Hot Mix Asphalt
Abbreviation for Hot Mixed Asphalt Concrete
Abbreviation for High Output
Abbreviation for Heated Oxygen Sensor — Detects exhaust rich or lean of oxygen of the following types:

  1. HO2S-1-1: Abbreviation for Bank One Sensor One Signal
  2. HO2S-1-2: Abbreviation for Bank One Sensor Two Signal
  3. HO2S-1-3: Abbreviation for Bank One Sensor Three Signal
  4. HO2S-2-1: Abbreviation for Bank Two Sensor One Signal
  5. HO2S-2-2: Abbreviation for Bank Two Sensor Two Signal
HodakaClick image for books on

A motorcycle manufacturer

  1. A colloquial term for a Harley Davidson motorcycle.
  2. A driver who persists in straddling both lanes at a slow speed so that it is impossible to pass him.


Straining of the ship that tends to make the bow and stern lower than the middle portion


Hog ring

Hog ringHog ring

A C-shaped wire used to secure a vehicle’s seat upholstery to the metal frame of the seat. Also called cushion clip

  1. A mechanism for lifting a whole vehicle or part of it.
  2. A lifting mechanism under cargo bodies that dump.
Hoist Chain
Chain manufactured strictly for a lifting application.
Hoisting rope
Flexible wire rope for lifting purposes, generally being of six strands with 19 wires in each strand and in most cases having a hemp rope at the center. Also called wire rope
The large spaces below deck for the stowage of cargo.

A mark-up of a certain percentage that the dealer pays the manufacturer on each new car that is added to his stock; this amount is rebated to the dealer after the car is sold
Hold Beams
Structural members placed in a hold, similar to deck beams, but having no plating or planking on them.
Hold ceiling
A covering usually of wood, placed over the tank top for its protection
Hold cycle
Maintaining steady hydraulic pressure during an ABS stop
A spring tension mechanism that holds a brake shoe against a backing plate

Hold down clamp
Hold-down pin, spring and retainer
The most common method of retaining a brake shoe to the backing plate. The pin passes through the backing plate and brake shoe. The spring and retainer are fastened to the pin, which holds the shoe against the backing plate
HoldenClick image for books on

An automobile manufacturer from Australia

One who ‘backs up’ or ‘holds on’ the head of a rivet while the point is being ‘driven,’ or upset.
Hold fitting
Hold-in coil
A separate relay coil, such as the hold-in winding in a starter solenoid, which is energized by contacts that close when the relay pulls in, to hold the relay in its energized position after the original operating circuit has been broken. Also called holding coil.
Holding coil
A separate relay coil, such as the hold-in winding in a starter solenoid, which is energized by contacts that close when the relay pulls in, to hold the relay in its energized position after the original operating circuit has been broken. Also called hold-in coil.
Holding Position
Holding winding
A part of a relay designed to hold it in the on-position. Compare Pull-in winding. Also called hold-in winding.
Hold-in winding
A part of a relay designed to hold it in the on-position. Compare Pull-in winding. Also called holding winding.
Hold-off valve
A unit which permits free fluid flow in either direction when the brakes are not applied, but prevents pressure buildup in one part of the brake system until pressure in the other part reaches a predetermined value.

Hold-open spring
Hold out
The ability of a surface to keep the top layer of paint from sinking in or being absorbed
Hole circle
Hole cutter
Hole cutting snips
Snips with pointed cutting blades for cutting holes in sheet metal material
Holed piston
A condition caused by severe detonation or preignition, where a hole is burned through the piston crown as a result of extreme heat or pressure.
Hole punch
  1. A tool like pliers used in autobody repair to form holes along the edge of a repair panel; the panel can then be plug-welded to the substructure at these holes
  2. A tool for poking holes in leather and fabric
A cylindrical-shaped saw for use with power tools, for cutting holes in sheet metal material, e.g., in car bodies for installation of aerials
Hole theory
Assumption that movement of a free electron from atom to atom leaves a hole in the atom it left, which is filled by another free electron
A void or hole in an adhesive or coating film, whether microscopic or normally visible
The action of forming a deeply crowned panel from a piece of sheet steel on a Hollowing block or a Shot bag, using special mallets and hammers
Hollowing block
A shaped wooden block on which a desired shape is produced by hammering
Hollow Pin Roller Chain
Chain manufactured using a bushing as the pin holding the pin link plates. This chain is generally used in pairs with the two strands running parallel and a thru rod tying them together.
Hollow-tube gasket
Sealing device made of rubber or plastic with tubular cross-section.
Holographic combiner
A semi-reflecting layer embedded in laminated windshield glass; used for head-up displays
Homofocal headlight
A type of headlight with two reflectors, the inner one has a shorter focal length than the main one
Being of a similar nature. Homogeneous liquids blend together completely; no part of either liquid remains separate.
A mechanical device which is used to create a stable, uniform dispersion of an insoluble phase (asphaltenes) within a liquid phase (fuel oil).
Homokinetic joint
An official recognition of a special version of a standard car as a production model, to make it eligible for racing
HondaClick image for books on
Honda automobiles
HondaClick image for books on
Honda motorcycles

An automobile and motorcycle manufacturer, Honda Motor Company, Limited in Japan which included the following automobiles:

  • Accord (1976-current)
  • Acty (1977-current)
  • Civic (1972-2008)
  • CR-V (1997-2007)
  • del Sol (1993-97)
  • Element (2003-07)
  • Fit (2007-08)
  • HR-V (1995-2005)
  • Insight (2000-06)
  • Legend (1985-current)
  • MDX (2003-06)
  • NSX (1990-2005)
  • Odyssey (1995-current)
  • Passport (1994-2002)
  • Pilot (2003-07)
  • Prelude (1978-2001)
  • Ridgeline (2006-08)
  • S2000 (2000-07)
  • Stepwgn (1996-current)
  • Stream (2000-current)
  1. To remove metal with a fine grit abrasive stone in order to meet precise tolerances.
  2. The device or tool which is rotated in a cylinder to remove slight imperfections in the cylinder wall.
Trucker slang for female county or state police officer as in ‘Just passed a honeybear in a tiajuana taxi takin’ pictures’.
A pattern of hexagonal shapes, like bees’ cells.

The situation that occurs when a lot (a run of manufactured products) is partially depleted and the remaining space is wasted because it cannot be used.
The precision machining process used to resurface bores and shafts in order to achieve close tolerances and a crosshatch pattern.

Honing stone
A tool used for the final smoothing operation, e.g., when repairing a cylinder wall
  1. The opening part of the vehicle body which covers the top of the engine in front engine vehicles. It may be hinged at the front, rear or sides. The British term is bonnet. In mid-engine cars the panel which conceals the engine is called the engine cover or access panel. In rear-engine cars the panel which conceals the engine is called a deck lid.
  2. A British term for the soft-top roof of a convertible.
Hood badge
An emblem reflecting the name or logo of the car manufacturer and is secured to the front end of the hood. Some are bolted or pasted flat to the front, others stand upright on fixed or pivoting rods.
Hood bar
A British term for one of at least four struts that support a roof. Usually made of tubular or sheet steel
Hood bow
A British term for one of at least four struts that support a roof. Usually made of tubular or sheet steel
Hood bump rubber
A thick rubber strip which is secured to the vertical panel on which the hood is lowered
Hood bumper
Hood landing panel
The panel on which the hood is lowered. It also houses the hood locking mechanism
Hood liner
A material secured to the underside of the hood to provide sound insulation. It is usually made of polyethylene, polypropylene, polyurethane, or a fabric of polyester
Hood lock
A mechanism which is made of a peg on the front end of the underside of the hood and a sliding latch on the panel above the radiator. The sliding latch is released by a lever under the hood or by a lever under the instrument panel in the passenger compartment.

Hood pin
A pin designed to hold a hood closed.
Hood pin kit
A pair of Hood pins and brackets which secure the hood of competition cars and ‘would-be’ competition cars
Hood pins
Pins designed to hold a hood closed.
Hood release
A device which releases the Hood lock. The trigger, located under the instrument panel in the passenger compartment, is attached to a cable which controls the hood lock.
Hood rod
A bar or rod which keeps the hood in an open position. The rod is located under the hood. Once the hood is raised, the rod is swung upright and the free end is placed in a notch or hole in the hood to keep it in place
Hood stick
An old British term for Hood bar
Hood support stay
A rod that is manually moved into place to keep the engine cover in an open position to facilitate engine compartment repairs
Hood tape
A fabric covered beading which keeps the hood on older cars from rubbing on the paint below them.
The curved, dropped section of a set of turned-down handlebars of a bicycle.

Hook Bolt
A ‘bent bolt’ having the unthreaded end bent to form a hook, such as a round bend, square bend, right-angle bend, or acute-angle bend hook bolt.
Hooke joint
Hooke universal
The curved, dropped sections of a set of turned-down handlebars of a bicycle.
Hook up
  1. To connect.
  2. To meet with someone.
Hooligan bike
A colloquial expression meaning damaged, out of order, or unrepairable as in Your engine is hooped.


Hopper Bottom
An open top cargo body capable of discharging its load through a bottom opening without tilting. Also called bottom dumps
Hopping up
Increasing engine performance through various modifications.
On 14 November 1899, August Horch (1868-1951) established the A. Horch & Cie. company in the Ehrenfeld district of Cologne, Germany where he developed his first car, which was completed at the beginning of 1901. The company moved to Reichenbach in Saxony in March 1902 and converted to a share-issuing company two years later. On May 10, 1904, A. Horch & Cie. Motorwagen-Werke AG was established in Zwickau. In 1932 Horch joined Audi. Models built between 1925 and 1932 models are classic cars.
Lying flat, not upright
Horizontal adjuster
A screw for adjusting the lateral aim of the headlight beam
Horizontal axis wind turbine
The most common type of wind turbine where the axis of rotation is oriented horizontally.

Horizontal draft carburetor
Horizontal draught carburetor
Horizontal keiretsu
A Keiretsu system where the keiretsu member companies have shareholdings in each other. The opposite is Vertical keiretsu. The member companies own relatively small chunks of shares in one another and are each centered on a core bank; the keiretsu system helps insulate company managements from stock market fluctuations and take-over attempts, allowing long-term planning and engagement in innovative projects; it is a key element of the automotive industry in Japan
Horizontally opposed engine
An engine possessing two banks of cylinders that are placed flat or 180 degrees apart. This configuration gives a lower center of gravity which improves handling. As well it has a lower hood height to improve aerodynamics. Also called a boxer engine.

Horizontal position
A weld performed on a horizontal seam at least partially on a vertical surface.
Horizontal Zero Line
A locating line at the top of the chassis frame as seen in side view. Also called waterline and datum line.
  1. Any opening chamber to intake air such as the entrance to a carburetor.
  2. A part of a cleat
  3. To line or square up
  4. HornHorn

    A device for sounding an alarm. On some entry level vehicles, a single horn makes a high pitch beep. On more expensive vehicles, the sound is made with two or more horns. The sound is made by an electrical charge which activates and deactivates a coil. The sound is then magnified by the shape of the horn. Large truck horns make a very loud noise because the sound is made by passing compressed air through the sounding device. A Claxton horn makes a sound that resembles the word A-hoo-gah. See blowing horn

Horn Baffle
Horn boss
A relatively large pad in the center of the steering wheel which sounds the horn when you press on it
Horn button
A relatively small button on the steering wheel or the end of the signal light lever which sounds the horn when you push on it
Horn circuit
An electrical circuit that provides the operator with an audible warning signal.
HornetClick image for books on

An automobile manufactured by AMC

Horn rim steering wheel
A steering wheel which had a thin metal strip on the inside of the rim. When the steering wheel was squeezed, the horn sounded.
Horn ring
A thin chrome ring which was smaller than the steering wheel which sounded the horn when pressed. This style was found on older vehicles.
Horn switch
An electrical device which engages the horn.
Horseless carriage
a term defined by the Horseless Carriage Club of America applying to cars built before 1915. (See also Antique).
(HP) A measurement of the engine’s ability to perform work. One horsepower is defined as the ability to lift 33,000 pounds one foot in one minute. To find horsepower, the total rate of work in foot pounds accomplished is divided by 33,000. If a machine was lifting 100 pounds 660 feet per minute, its total rate of work would be 66,000 foot pounds per minute. Divide this by 33,000 foot pounds per minute to arrive at 2 horsepower. In metric terms, it is the ability to raise 250 kilograms a distance of 30 centimetres in one second. It is also equal to 745.7 watts.

Horsepower Watts ||| KiloWatts Horsepower
1 745.7 ||| 1 1.3
2 1491.4 ||| 2 2.7
3 2237.1 ||| 3 4.0
4 2982.8 ||| 4 5.4
5 3728.5 ||| 5 6.7
6 4474.2 ||| 6 8.0
7 5219.9 ||| 7 9.4
8 5965.6 ||| 8 10.7
9 6711.3 ||| 9 12.1
10 7457 ||| 10 13.4
20 14914 ||| 20 26.8
30 22371 ||| 30 40.2
40 29828 ||| 40 53.6
50 37285 ||| 50 67.1
60 44742 ||| 60 80.5
70 52199 ||| 70 93.9
80 59656 ||| 80 107.3
90 67113 ||| 90 120.7
100 74570 ||| 100 134.1
200 149140 ||| 200 268.2
300 223710 ||| 300 402.3
400 298280 ||| 400 536.4
500 372850 ||| 500 670.5
600 447420 ||| 600 804.6
700 521990 ||| 700 938.7
800 596560 ||| 800 1072.8
900 671130 ||| 900 1206.9
1000 745700 ||| 1000 1341.0
Horsepower Motor
Horsepower screw
A screw in the cover of adjustable Wastegates to vary the spring height, which adjusts boost pressure; screwing down adds HP but may destroy the engine
Horsepower weight factor
Horsepower-weight factor
The relationship between the total weight of the vehicle and the horsepower available. By dividing the weight by the horsepower, the number of pounds to be moved by one horsepower is determined. This factor has a great effect on acceleration, fuel consumption, and all around performance.
Horseshoe clip

horseshoe clipHorseshoe clip

A wire spring retainer used to secure an inside door handle in place.

A flexible tube used to convey liquid. In most automobiles, hoses connected independent components like the radiator, Water pump, and Heater.

Hose clamp
An adjustable metal ring, wire, or band placed around a hose where it connects to a metal pipe, to prevent leaks and to keep the hose in place. Hose clamps are tightened in one of three ways. In single wire clamps, it is tightened by spring tension of the clamp. In worm-gear clamps, by a worm screw. In strap-and-bolt clamps, by a screw. The British term is hose clip.
Hose clamp installer
A special tool for the installation of ear-type clamps, used e.g., on some types of CV joint boots, filters, cooling systems, and vacuum lines
Hose clamp pliers
A special tool used to remove and install hose clamps
Hose clip
A British term for Hose clamp
Hose clip installer
British term for Hose clamp installer
Hose clip pliers
British term for Hose clamp pliers
Hose Coupler
Hose pinch-off pliers
A special tool to pinch off hoses when servicing the cooling system; pivoting jaws squeeze hoses shut so there is no need to drain the system
Hose Shark Tooth Pliers
Hostling Tractor
Tractor used for moving trailers to and from the dock and around the yard.
Connected to the battery positive terminal, energized
Hot cap
The conventional method of retreading in which uncured rubber is added to a buffed Casing and cured in the mold at temperatures of approximately 143°149°C. This temperature allows uncured rubber to flow in the matrix forming the tread design during vulcanization.


A brand of vehicle of which the 1925-1948 models, with required application, are classic cars.
Hotchkiss drive

Hotchkiss driveHotchkiss drive

The method of connecting the transmission Output shaft to the differential Pinion by using open driveshafts. The driving force of the rear wheels is transmitted to the frame through the rear springs or through link arms connecting the Rear axle housing to of the vehicle. Combines both Steering axis and Camber angles.

Hotchkiss suspension
A live-axle Rear suspension in which Leaf springs handle both the axle’s springing and its location.

Hot dip
To coat metal parts by immersion in molten metal, such as tin or zinc
Hot-dip aluminizing
The deposition of aluminum coatings by hot dipping
Hot-dip galvanize
To apply a zinc coating by hot dipping
Hot dry rock
Heat energy residing in impermeable, crystalline rock. Hydraulic fracturing may be used to create permeability to enable circulation of water and removal of the heat.
Hot forging
Heating metal to red-hot temperatures or temperatures above the recrystallization point to soften it before shaping a fastener. Hot forging is primarily used when the diameter of the metal is too large for cold forming or the quantity required is too small to economically set up a cold-forming machine.
Hot Forming
Working operation such as bending and drawing sheet and plate, forging, pressing, and heading, performed on metal heated to temperatures above room temperature.
Hot Fuel
Expanded diesel fuel or gasoline that is sold at retail pumps at temperatures higher than the century-old government standard of 15.5°C. At the 15.5°C standard, a gallon of fuel delivers a certain amount of measurable energy, or BTU. But when expanded by higher temperatures, that same amount of fuel actually delivers less energy. The warmer the fuel, the less BTU and fewer miles to the gallons a vehicle will receive.
Hot gas
The state of the refrigerant between the compressor and the condenser
Hot gas bypass
Piping system in refrigerating unit which moves hot refrigerant gas from condenser into low-pressure side.
Hot gas defrost
Defrosting system in which hot refrigerant gas from the high side is directed through evaporator for short period of time and at predetermined intervals, in order to remove frost from evaporator.
Hot Gas Tube System
Hot gas welding
A welding process involving the joining of thermoplastic materials by softening with a jet of hot air, then joining them at the softened points
Hot grip
Electrically heated handlebar grips used on snowmobiles
Hot hatch
High-performance hatchback
Hot idle compensator
A small air valve that allows fresh air to enter the manifold and lean the mixture when the engine is hot
Hot in-place recycling
Crews heat up and grind off the top few inches of pavement, which is thoroughly mixed with new material and put back down. This process, chiefly used on high-volume roads, creates a road bed that closely resembles a new road in consistency and strength.
Hot junction
That part of thermoelectric circuit which releases heat.
HOT Lanes
Abbreviation for High Occupancy Toll lanes, which are special lanes on a multi-lane road which can be used free of charge by vehicles with enough occupants to constitute a car pool, but which are subject to a toll for other vehicles. In some cases these lanes can be used only by vehicles that have special electronic tags and there are no facilities to pay tolls by means of cash. HOT lanes are a relatively new development.
Hot lash
The valve adjustment on a engine equipped with solid lifters
Hot plug
A spark plug which has a long insulator nose which absorbs more heat and dissipates heat slowly. A colder plug is used in a hot engine while a hot plug is used in a cold engine. Thus if the plugs are fouling too much, try a hotter plug. If the plugs are coming out white, try a colder plug. The ideal color of the center insulator nose should be a light chocolate brown.
Hot rod
A production car that has been modified by the owner in the attempt to increase acceleration and top end speed. Although the term can be applied to any modified car, it is usually reserved for vehicles produced from 1930 to 1940’s. Typically the engine is modified, and some body panels removed. Many were painted with a design of flames behind the front wheels to give the appearance that this vehicle was hot — thus the name.
Hot Shot
  1. Colloquial term for a local freight hauler
  2. Colloquial term for a one ton truck equipped with a fifth wheel for pulling light weight trailers.
Hot soak
Occurs when the engine is topped during hot weather or after it has been run long enough to be fully warmed up; also the period during which the phenomenon known as percolation occurs
Hot spark plug


Hot spot
  1. Refers to a comparatively thin section or area of the wall between the intake and exhaust manifold of an engine, the purpose being to allow the hot exhaust gases to heat the comparatively cool incoming mixture.
  2. Also used to designate local areas of the cooling system which have above average temperature.
Hot spraying
A spray process in which paint is preheated in a paint container so that its viscosity is reduced and it can be atomized without being diluted with a solvent
Hot start
The starting of a hot engine may be difficult if it has been stopped for a few minutes; the accumulation of gasoline vapor in the air filter and inlet manifold, caused by the rise in engine temperature when left standing when hot, can be dissipated by slowly pressing the accelerator right down and turning the engine over until it fires
Hot start enrichment
A fuel mixture enrichment when starting a hot engine
Hot starting


Hot-start pulse relay
A fuel injection component which operates the cold-start valve intermittently to improve starting when the engine is hot; installed in the cold-start valve circuit in some CIS-equipped engines
Hot water and low-pressure steam boiler
A boiler furnishing hot water at pressures not more than 30 psi gauge (308 kPa) or steam at pressures not more than 15 psi gauge (205 kPa)
Hot water heating system
System in which water is circulated through heating coils.
Hot water vacuum valve
A vacuum actuated valve which controls the flow of coolant through the heater core
Hot wax
Wax-based material used for Hot-wax flooding
Hot-wax flooding
A special cavity-sealing process developed by Volkswagen, which uses a solvent-free wax injected into the cavities of bodies preheated to 60°C
Hot-wax flooding unit
A device for Hot-wax flooding consisting of a preheating zone, a flooding zone and a drip-off zone
Hot wire
  1. The positive wire coming from the battery or generating system.
  2. Resistance wire in an electrical relay which expands when heated and contracts when cooled.
  3. Electrical lead which has a voltage difference between it and the ground.
  4. As a verb, it indicates the starting procedure when by-passing the ignition key and normal starting procedure.
Hot-wire airflow meter
A constant-temperature hot-wire sensing device, used in electronic fuel injection systems, which measures the rate of a mass airflow into the engine by measuring the current needed to keep the hot wire at the same temperature
Hot-wire element
An element in a hot-wire air-flow meter
hot wire relay
Heat-operated electrical control used to open or close a refrigeration system electrical circuit. This system uses a resistance wire to convent electrical energy into heat energy.
Hot-wire sensor
Hour capacity
(HOS) A U.S. Department of Transportation safety regulations which govern the time of operation of commercial vehicle drivers engaged in interstate trucking operations.
House bridge
An erection fitted on the upper or superstructure deck of a ship. The officers’ quarters, lounge are usually located in the bridge house
Household Goods cargo
Truck cargo consisting of uncrated household or office furniture, band equipment, theatrical equipment, and trade show displays.
Keeping the warehouse presentable, organized, and safe for all parties.
House panel
  1. The outer sleeve through which a brake or gear cable is pulled. The housing transmits an equal push to counter the pull on the inner cable. Traditional housing consists of a tight spiral of steel wire, usually coated with plastic. Newer versions have synthetic liners to reduce friction.
  2. A container or casing for mechanical components such as bearings, gears, etc.
Housing banjo
Housing split


Abbreviation for high-occupancy vehicle — A vehicle carrying two or more passengers used on marked commuter lanes. Examples include car pools, vanpools, buses, and mini-buses. Transportation systems may encourage HOV use by having designated HOV lanes.

A ground vehicle that is supported by a cushion of air to reduce friction. As well as traveling on the land, hovercraft can travel on the sea or swampy terrain.
HOV Lane
Abbreviation for High Occupancy Vehicle Lane which is an exclusive road or traffic lane limited to buses, vanpools, carpools, emergency vehicles, and in some cases, single occupant motorcycles. HOV lanes typically have higher operating speeds and lower traffic volumes than adjacent general purpose lanes. HOV lanes have proven to be successful in major metropolitan areas across the US ; however, their full effectiveness is usually not realized until about one to two years after implementation.
Abbreviation for horsepower.
Abbreviation for High Pressure Cutoff
Abbreviation for High-Performance Computer Architecture designating a type of computer chip.
Abbreviation for High Pressure Liquid
The point, usually called out on a full-sized, side-view body draft, where the driver’s hip socket rests near the junction of the front-seat cushion and the seatback. See Hard Points
  1. Abbreviation for High Performance System
  2. Abbreviation for High Pressure Vapor
Abbreviation for Human Powered Vehicle.
Abbreviation for high speed direct injection for a diesel engine
Abbreviation for High Swirl Combustion
Abbreviation for High speed road monitoring survey
  1. Abbreviation for Hardtop.
  2. Abbreviation for High-tension
HT circuit
HT distributor
A distributor, in electronically controlled ignition systems, which has no controlling functions or advance mechanism
high temperature gas-cooled reactor
HT lead
HT outlet
Abbreviation for Hydraulic unit
  1. On a bicycle, the center of a wheel consisting of a shell to which spokes attach and contains an axle along with two sets of bearings, bearing Cones, Lockwasher, Locknuts, and parts for attaching the wheel to the frame.
  2. The base of a wheel (e.g., steering wheel, drive or driven wheels) with studs protruding from its face upon which the wheel itself is mounted to an automotive vehicle.
  3. A rotating component at the center of a wheel that contains the wheel bearings to which the rest of the wheel are attached. It is connected to, or integral with, the brake drum or rotor.
Hubbed drum
A brake drum mounted on a hub.
Hub brake
Any type of brake (disc, drum, or Coaster) that operates through the wheel hub rather than the rim.
The covering that fits over the end of the wheel spindle to keep dust and water away from the wheel bearings and brakes. It is often a styling feature, but it also acts as a good container for keeping the Lug nuts from being lost when changing tires. When a vehicle becomes stuck in the snow, it can also be used as a temporary shovel. Also called wheel cover.


Hub cap


Hub carrier
  1. A part of the suspension system which carries a rear wheel hub on a front-wheel drive vehicle, or on a rear-wheel drive vehicle with independent rear suspension.
  2. Another term for Steering swivel
Hub cassette
Hub-center steering
Steering system in which the wheel pivots about its center point; the axle is normally fixed
Hubcentric fit
A spigot mounted wheel
Hub flange
The portion of a bicycle hub into which the spokes are seated.
Hub freewheel
Hub height
In a horizontal-axis wind turbine, the distance from the turbine platform to the rotor shaft.
In 4-wheel-drive vehicles, it is inefficient to have the front wheels connected when not needed. Most older vehicles required a person to get out and manually switch each front hub. Now these hubs can be changed remotely with a switch inside the vehicle.

A register mounted on the axle hub which shows the distance the vehicle traveled. It is popular to record mileage for leasing of vehicles or tires particularly on trailers, since there is no other odometer present.
The instrument on the wheel of a tractor used to record mileage.
Hub plate
The central element of a clutch driven plate which carries the splined hub
Hub puller
A special tool, of both jaw and slide hammer design, used to remove wheel hubs on vehicles by a pulling action
Hub spacing
The distance from one outer cone to the other along the axle. Front bicycle hubs have a standard width of 100mm. Rear hubs on older road bikes which are set up for freewheels generally have a width of 126mm. More recent rear hubs set up for cassettes have a width of 130mm.
An abbreviation for Heads up display which is a system of mounting gauges so that the read-out is shown on the windshield. In this way the driver does not have to take his eyes off the road to see how his vehicle is performing.
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A brand of vehicle of which the 1929 Series L is a classic car. All 1948-49 models are milestone cars. The 1951-54 Hornet models are milestone cars.

Body of a ship which floats on the water including shell plating, framing, decks, bulkheads.
A brand of vehicle of which the 1925-1948 models, with required application, are classic cars.
Device used to add to and control humidity.
Humidifying tower
The air saturator tower in salt spray test chambers
Electrical control which is operated by changing humidity.
The moisture or dampness in the air. Usually refers to an uncomfortably high level of humidity.

Humidity chamber
A test chamber for simulating tropical and subtropical conditions
(short for humidity index) is a number which combines the air temperature in Celsius and the amount of humidity in order to give a single number to represent the perceived discomfort of weather that is hot and humid. It was devised by Canadian meteorologists and first used in 1965. The humidex is widely used in Canada and has been accepted in a number of other countries.

Range of humidex Degree of comfort
Less than 29 No discomfort
30 to 39 Some discomfort
40 to 45 Great discomfort; avoid exertion
Above 45 Dangerous
Above 54 Heat stroke imminent

The humidex is calculated with the following formula
Humidex = (air temperature) + h
h = (0.5555)*(e – 10.0);
e = 6.11 * exp(5417.7530 * ((1/273.16) – (1/dewpoint)))

HummerClick image for books on

A large SUV produced by General Motors which is based on the military High Mobility Multipurpose Wheeled Vehicle (HMMWV or Humvee). Models included are

  • H1 (1993-2006)
  • H2 (2003-07)
  • H3 (2006-08)
  • H3 Alpha (2008)
  • H3x (2008)
A raised portion on the rim bead seat of passenger car wheels, retaining the beads of an insufficiently inflated tubeless tire on the bead seats, thereby preventing the tire beads from jumping into the rim well.

Hump mode
An operating condition where the transmitted torque in a viscous coupling rises to a value several times higher than the value produced in the so-called Viscous mode, due to internal clamping, i.e., metal friction of the coupling discs
Hump rim
Designation for a rim featuring a safety contour (Round hump, Flat hump, combination hump) either on the outer or on both bead seats. This protection is particularly important with tubeless tires, where sudden deflation can occur if the tire beads leave the bead seats and drop into the well. Compare Hump and Safety bead seat
(cwt) An obsolete unit of weight measurement, used in some classic-car manuals. 1 British cwt = 5080 grams; 1 US cwt = 4535 grams
  1. The uneven running of an engine, due to air/fuel mixture being too rich.
  2. The action of some automatic transmissions when a vehicle is climbing a hill. The transmission constantly shifts between fifth gear and fourth gear
  3. Erratic variation of the speed of the governor when it overcompensates for speed changes.
Hunting tooth
An extra, odd tooth on a gearwheel, designed to ensure the same teeth do not always mesh together, thus reducing wear
Hurst six-speed shifter
Upgraded shifter for manual transmissions which make the distance between gears shorter. The power band is more continuous from the bottom of first gear to the top of sixth. This means that when you shift, the amount of acceleration you experience will be more even throughout all the levels of the transmission. The result is that you can make the car accelerate faster and gain more control (through enhanced consistency) in turns or any application of power. Hurst also manufactures many other shifters with 2 to 6 gears for a variety of cars. Linda Vaughn has been their spokeswoman for many years.
See Fidley Hutch.
Abbreviation for heating, ventilation, and air conditioning system
H valve
A type of expansion valve used by Chrysler Corp
Abbreviation for Heavy Van (e.g., Mitsubishi Canter).


Abbreviation for highway.

An alternative power plant that combines a small internal combustion engine and an electric motor to get maximum power with minimum emissions and maximum fuel economy.
Hybrid car
A car with a Hybrid propulsion system.

Hybrid-Electric Vehicle
(HEV) A vehicle that is powered by two or more energy sources, one of which is electricity. HEVs may combine the engine and fuel system of a conventional vehicle with the batteries and electric motor of an electric vehicle in a single drivetrain.
Hybrid pad sets
Brake pad sets that contain an organic pad for one side of the rotor, and a semi-metallic pad for the other
Hybrid propulsion
Two distinct but interdependent forms of propulsion, such as an electric motor and an internal combustion engine, or an electric motor with battery and fuel cells for energy storage, or pedal power and an electric motor.
Hybrid technology
Film circuits combined with integrated circuits, used especially for trigger boxes or electronic control units
Hybrid transmission line
A double-circuit line that has one alternating current and one direct circuit. The AC circuit usually serves local loads along the line.
Hybrid Vehicle
A vehicle that uses two or more forms of Propulsion. Some examples are the following

Hybrid Vehicles
Cadillac Escalade Hybrid Chevrolet Malibu Hybrid Chevrolet Tahoe Hybrid Ford Escape Hybrid
GMC Yukon Hybrid Honda Civic Hybrid Lexus GS 450h Lexus LS 600h L
Lexus RX 400h Mercury Mariner Hybrid Nissan Altima Hybrid Saturn Aura Green Line
Saturn Vue Green Line Toyota Camry Hybrid Toyota Highlander Hybrid Toyota Prius
A RockShox® suspension design that uses air springs, negative springs (coil), and an oil bath.
A RockShox® suspension design that uses coil springs, negative springs (coil), and an oil bath.
Hydragas suspension
Hydration Pack

Hydration PackHydration Pack

A water filled back pack for cyclists and hikers. It has a tube placed within reach for supplying water for the user. Trade names are Camelbak® and Hydrapak®

  1. When a quantity of water, oil, or other fluid is forced along one end of a line, it also forces against the other end of the line. Because these fluids (unlike a gas) cannot be compressed, when they are forced into a smaller cylinder they multiply the amount of force. Thus a driver can apply a small amount of force on the pedal or lever and a great amount of force is applied to the brake. Used in Power steering, clutches, and brake systems.
  2. When used as a verb, it means that oil or excessive gasoline has entered the combustion chamber so that when compression takes place, the fluid cannot be compressed. Something has to give and it is usually the Connecting rod that bends. It is found in the expression, the engine hydrauliced.
Hydraulic accumulator
A part of the hydraulic system which is charged by the fluid pump, absorbs fluctuating fluid delivery, stores fluid at pressure, and can provide a rapid flow of fluid under pressure.
Hydraulic actuator
Unit in an anti-lock brake system that can increase brake pressure, decrease brake pressure, or hold brake pressure steady based on signals it receives from the control module
Hydraulic actuators
The hydraulically operated struts which control the movement of the wheels in an active ride suspension system
Hydraulically-activated brakes
A motorcycle system where the brakes use hydraulic fluid instead of a cable. When the lever/pedal is squeezed/pressed, hydraulic fluid forces the pistons to put pressure on the brake pads which rub against the brake disc and cause enough friction to stop the bike. A master cylinder that contains the hydraulic fluid sits on the handlebar near the brake lever.
Hydraulically-assisted brakes
Hydraulically-activated clutch
Found in a motorcycle, the clutch is engaged/disengaged via hydraulic fluid instead of a cable. When the lever is squeezed, hydraulic fluid forces the pushrod to disengage the clutch. A master cylinder that contains the hydraulic fluid sits on the handlebar near the clutch lever.
Hydraulically-assisted clutch
A clutch operated by hydraulic pressure.
Hydraulically operated power booster
A power booster that uses hydraulic pressure to assist the driver in the application of the brakes. This hydraulic pressure usually comes from the power steering pump or an electro-hydraulic pump
Hydraulic assisted brakes
Hydraulic booster
A master cylinder containing a separate hydraulic chamber and Spool valve operated by power steering fluid. Hydraulic pressure in the booster pressure chamber operates the master cylinder piston.
Hydraulic brakes
Hydraulic brake booster

Hydraulic brake boosterClick image to supersize

Hydraulic pressure supplied by the power steering pump, or a separate hydraulic pump, which is used to assist in applying the brakes; used on cars and on some trucks

Hydraulic Brake Power-assist Unit
Hydraulic assisted brakes
Brakes operated by hydraulic pressure.

Hydraulic brake system
A brake system in which brake operation and control uses hydraulic pressure.

Hydraulic braking system
Brakes operated by hydraulic pressure.

Hydraulic circuit
  1. Part of the main brake system that includes two of the four wheel brakes and operates independently of the other two wheel brakes; all vehicles have a primary and secondary hydraulic circuit
  2. The path of hydraulic fluid from the master cylinder to the wheels, through all valves, lines, hoses, and fittings.
Hydraulic clutch
A system which uses hydraulic pressure to disengage the clutch plates.
Hydraulic control block
A Control valve assembly
Hydraulic control unit
The portion of an anti-lock brake system that houses the solenoid valves and electro-hydraulic pump
Hydraulic-Electronic Unit Injector
(HEUI) A type of unit injector actuated by engine oil pressure rather than the camshaft. A very high oil pressure (up to 3,000 psi) is created by a separate oil pump. This high pressure is routed to every injector through a gallery. The engine’s Electronic Control Module varies the pressure in response to engine speed and other parameters.
Hydraulic fluid
A special oil used in hydraulic systems, such as power steering, self-leveling suspension, to operate the system of master and slave cylinders. Also compare brake fluid and Automatic transmission fluid
Hydraulic fracturing
Fracturing of rock at depth with fluid pressure. Hydraulic fracturing at depth may be accomplished by pumping water into a well at very high pressures. Under natural conditions, vapor pressure may rise high enough to cause fracturing in a process known as hydrothermal brecciation.
Hydraulic hoist

Hydraulic hoistHydraulic hoist

A device for lifting a vehicle from the ground. Usually found in service bays to facilitate inspection of the running gear and exhaust system or for removing fluids.

Hydraulic hood
British term for Hydraulic top
Hydraulic jack
A device used to lift a vehicle by using hydraulic pressure.
Hydraulic lift
A device used in a service garage to raise a vehicle so that a mechanic can look at or repair components under the vehicle.
Hydraulic lifter
Hydraulic modulator
A device which regulates hydraulic fluid pressure in an ABS.

Hydraulic piston
A piston in a cylinder, acted upon by or acting on a hydraulic fluid.
Hydraulic Power Unit
Hydraulic pressure
The force per unit area exerted in all parts of a hydraulic system by a liquid.
Hydraulic pressure pump
An engine-driven pump which supplies oil under pressure to operate, e.g., power brakes or power-assisted steering
Hydraulic Retarder
A transmission-mounted hydraulic device which assists in slowing down a vehicle.


  1. Branch of physics having to do with the mechanical properties of water and other liquids in motion.
  2. The study of pressure and flow in liquids. A Hydraulic jack uses oil under high pressure to lift large objects more easily.
Hydraulic service bench
Bench equipment used when disassembling, assembling, and testing brake calipers.
Hydraulic tappet
British term for Hydraulic valve lifter
Hydraulic top
A convertible top which is raised and lowered by a hydraulic system; depending on engineering, a hydraulic top can operate fast, silently, and with tremendous power.

Hydraulic unit
(HU) Valve unit for an anti-lock brake system.
Hydraulic valve lifter
A Lifter that uses hydraulic oil pressure to maintain no Clearance between metal parts so that valve noise is reduced. Also it reduces wear on the valves and eliminates periodic valve adjustments.
Hydraulic wedge
A Hydraulic jack with ends designed to reach behind dented double panels and to press them back into shape by the hydraulic action of the wedge-shaped ends
Hydraulique Minerale
Hydroactive suspension
(HC) A Compound made up of hydrogen and carbon (e.g., gasoline, Petroleum products, etc.). Hydrocarbons are also found when gasoline is burned in an engine and thus produce visible Smog even though hydrocarbons make up only 0.1% of emissions.

Hydrocarbon engine
An engine using Petroleum products, such as gas, liquefied gas, gasoline, kerosene, or fuel oil as a fuel.
Hydrocarbon plastics
Plastics based on resins made by the polymerization of monomers composed of carbon and hydrogen only
Organic compounds containing only hydrogen and carbon atoms in various combinations.
(HCFC) Chemicals composed of one or more carbon atoms and varying numbers of hydrogen, chlorine, and fluorine atoms.
Hydrodynamic clutch
Hydrodynamic torque converter
Hydroelectric power
Hydro-electric power
Electricity produced by using the Kinetic energy of water.
(HFC) A group of man-made chemicals composed of one or two carbon atoms and varying numbers of hydrogen and fluorine atoms. Most HFCs have 100-year Global Warming Potentials in the thousands.
A vessel which skims the surface of the water and the shaped pieces on the bottom of the vessel which act like water wings to give it lift.
(H) A gas formed of the single element hydrogen. It is considered one of the most active gases. When combined with oxygen, it forms a very clean flame which, however, does not produce a very high temperature or very much heat.
Hydrogen embrittlement
A process which results in a decrease of the toughness or ductility of a metal due to absorption of hydrogen
Hydrolastic suspension
A proprietary suspension system incorporating a conical rubber spring compressed by hydraulic pressure; this system also provides a hydraulic interconnection between front and rear wheels on one side of the vehicle.

Hydromechanical Injection
An injection system in which mechanical parts work through hydraulic pressure to meter and time the injection of fuel. No electronics are incorporated into hydromechanical injection systems.
  1. Floating instrument used to measure specific gravity of a liquid.
  2. A device to determine the weight of a liquid. It is used to test battery electrolyte and the percentage of coolant in the cooling system.
Heating system which circulates a heated fluid. usually water, through baseboard coils by means of a circulating pump which is controlled by a thermostat.
  1. When your tires start to float on top of water, causing them to lose contact with the road’s surface
  2. When a tire rolls upon a layer of water instead of staying in contact with the pavement. Hydroplaning occurs when all of the water on the pavement cannot be displaced from under the tire tread.


A phenomenon of driving when water builds up under the Tire tread, causing it to lose contact with the road. Caused by speed, water depth, tread depth, and inflation pressure. Slowing down will usually restore normal tire contact with the road. Also called Aquaplaning.

Hydropneumatic suspension
A Suspension system which uses a gas and a liquid which are separated by a flexible Bladder. The setup causes the suspension to maintain a preset height. Used in Citroën cars.
A hydraulically operated system that can excite vibrations of various frequencies in a car; serves to find and eliminate noise sources
Hydrostatically inflate
To inflate with water instead of air.

Hydrostatic drive
Hydrostatic gauge
Gauges, such as gas tank gauge, in which the depth of the gas in the tank controls the air in the connecting line to the instrument, which registers the depth on a scale or dial
Hydrostatic steering
A power steering system without mechanical steering links, but is controlled entirely by hydraulics
Hydrostatic test
Pressure test using water
Hydrostatic transmission
A drive by means of hydraulic motors, particularly where the drive is to each wheel of an off-road vehicle
Hydroxyl radical
(OH) An important chemical scavenger of many trace gases in the atmosphere that are greenhouse gases. Atmospheric concentrations of OH affect the atmospheric lifetimes of greenhouse gases, their abundance, and, ultimately, the effect they have on climate.
Instrument used to measure degree of moisture in the atmosphere.

  1. Something that tends to absorb moisture
  2. Ability of a substance to absorb and release moisture and change physical dimensions as its moisture content changes.
Hypoid axle
A driving axle with a hypoid gear
Hypoid gear

Hypoid gearHypoid gear

A type of Spiral bevel gear in which the Drive pinion shaft is located below the center of the Ring gear. This setup is used to lower the height of the driveshaft and thus lower the floor of the vehicle.

Hypoid oil
A special lubricant for hypoid gears
  1. The energy lost and not returned, when tire materials are subjected to stress in any direction. Lost energy is converted to heat through molecular interaction, and since rubber has poor thermal conductivity, internal temperatures of a tire can build up rapidly under repeated flexing.
  2. The damping provided by elastomer springs.
  3. An oscillator effect wherein a given value of an operating parameter may result in multiple values of output power or frequency.
Hysteresis loop
The pattern that is formed or described by the magnetic flux intensity as a magnet approaches a magnetic object.
hysteresis loss
The resistance offered by materials to becoming magnetized, reduced by using silicon steel laminations
HyundaiClick image for books on

An automobile manufactured in South Korea which includes Accent (1995-2008), Azera (2006-07), Elantra (1992-2008), Entourage (2007), Excel (1985-94), Santa Fe (2001-07), Scoupe (1991-95), Sonata (1989-08), Tiburon (1997-2007), Tucson (2005-07), Veracruz (2007), XG300 (2001), and XG350 (2002-05)

Hy-vo chain
A very strong chain made up of toothed plates positioned side by side and held together by pins.


Abbreviation for Hertz. A unit of frequency equal to one cycle per second.