Automotive Glossary

Automotive Glossary

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Health And Safety at Work Act 1974.(UK)"



Half Shafts

Shafts by which power is transmitted from final drive to driven wheels in an enclosed axle.

Hall Generator

An electronic pulse generator using the Hall effect of a semiconductor to provide information to the ignition amplifier or ECU on engine position and speed.

Hall IC

Integrated circuit as part of a Hall sensor.

Hall Sensor

An electronic pulse generator using the Hall effect of a semiconductor to provide information to the ignition amplifier or ECU on engine position and speed. Also used for sensing road speed etc.


A description of a series of gases such as argon.


Hand operated parking brake usually with a mechanical linkage. Also forms the reserve or emergency brake on many vehicles.

Handbrake Cable

A cable that operates the brakes when a lever is pulled.

Handbrake Linkage

Cables or rods used to operate the parking/handbrake.

Hard Disk

A storage device that holds large amounts of data.


A chemical specifically designed to ensure cure of a paint finish, filler, stopper, resin or adhesive. Also, another name for an activator.


The physical components of a computer system.


A physical connection between two or more electrical devices.

Harmonic Balancer

Rotating or oscillating engine balance shaft.


The collection of vehicle cables wound together with an insulation tape. Also known as a 'wiring loom'.


Risky. Potential to harm people or property.


The development of a cloudy area in the paint film or in a clear liquid.


(1) Hydrocarbon. (2) High compression.

Head Gasket

Seal between cylinder block and cylinder head.


Viewing a repaired/re-painted area from an angle that is perpendicular (at 90°) to the car.

Head-up Display

Projection of instruments onto the windscreen so that the road and the instruments can be seen at the same time by the driver.

Header Tank

The expansion tank at the top of a coolant radiator, which can be part of the radiator or a separate tank.


Vehicle lighting that provides illumination of the road for the driver. Usually consists of switched main and dipped beams.

Headway Sensor

A device usually fitted in the front grill of a vehicle that in conjunction with a transmitter senses distance in front of the vehicle. Often part of an active cruise control system.


A form of energy in all materials that can be used to do work.

Heat Exchanger

A device for transferring heat from one system or place to another.

Heat Range

Applies to spark plug construction where the rate of heat loss from the plug nose is controlled by the length of the insulation. Spark plugs are given a rating from hot to cold to classify the heat range and application. The plug tip temperature is controlled to keep the tip and electrodes clean.

Heat Sink

A plate to which electronic components are attached to dissipate heat.

Heater Matrix

Small radiator used to exchange heat from the coolant to the vehicle cabin.


Heated Exhaust Gas Oxygen Sensor. Also EGO Exhaust Gas Oxygen Sensor, EOS Exhaust Oxygen Sensor and Lambda sensor. Provides information to the fuel system ECU on the oxygen content in the exhaust gas.


High Energy Ignition. A distributor ignition system using electronic control of the coil secondary output.

Helical Gear

A gear with teeth cut at an angle.

Helical Rotor

A turbine or compressor in a turbocharger often has vanes that are helically shaped.

Helical Spring

Metal spring used in vehicle suspension. Also known as a coil spring.


A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball - a hemisphere is half a sphere


A fuel used in research tests as a comparison when determining the octane rating of fuels. Octane value of zero.


The number of oscillations per unit of time. The SI unit for frequency is the Hertz which equals one oscillation per second.


Short for hexagonal.



Hide Mallet

Soft hammer made of hide (leather). Plastic types are also used.

Hiding or Hiding Power

(See 'Opacity')

High Boilers

Solvents with boiling points above 100 degrees Celsius.

High Lift Cam

A special cam profile used on performance engines to increase the opening size of a valve.

High resistance

An unwanted resistance in a circuit that causes it to operate incorrectly.

High Solids

Paints are described as having high solids when they contain more than 50-60% solids. High solids paints have lower VOC's.

High Tension

The term used for the high voltage in the secondary circuit of the ignition system.


Hall generator. A sensor using a Hall effect to provide signals to an ECU.


Heated Oxygen Sensor


To lift something or a term used to describe a vehicle lift or ramp.

Hold-in Winding

A winding in a starter motor solenoid that holds the switch contacts together and the drive pinion in mesh during engine starting.


The ability of a surface to keep the topcoat from sinking in and causing a decrease in appearance or gloss.


Uniform in structure or composition throughout. This is usually used to refer to a fuel air mixture in a cylinder that is a 'perfect' mixture of fuel and air.


A light grinding process applied to cylinder bores in preparation for the fitting of new pistons.

Hooke's Joint

A drive shaft universal joint consisting of two yokes and a cross bearing. Also Cardan joint.

Horizontally Opposed

An engine configuration where cylinder pairs are fitted on opposite sides of the crankshaft. Sometimes referred to as 'Boxer' engines.


A measure of power equivalent to 0.746 Kilowatts. Defined by a rate of doing work of 33,000 foot pounds per minute (550 foot pounds per second).


Heated Oxygen Sensor.

Hose Clamp

Simple ring type clamp to seal a hose onto a pipe.

Hot Idle Compensator

A device to change idle or mixture settings when an engine is hot.

Hot Spray

The technique of applying paint at elevated temperatures. The elevated temperature reduces the viscosity so that higher solids materials can be sprayed, and allows application with less solvent.

Hot Stamping

A machine forging process using a series of dies to create the completed shape.

Hot Wire

A small thin wire that is heated an placed in an air flow. The change in temperature is used to determine the rate of air flow.




High Tension

HT Cables

High tension leads (high voltage) used to supply the spark.

HT Leads

High tension leads (high voltage) used to supply the spark.


Centre of a wheel or gear or similar.

Hub Nut

Main nut that secures a wheel hub.


The quality by which colours are distinguished from one another, such as">a red from yellow, blue, green, or purple, and all shades in between.


Uneven running of an engine, usually when the mixture is over rich.


Heating, ventilation and air conditioning.

HVLP (High Volume, Low Pressure)

Describes a paint gun that uses a high volume and low pressure of atomising air to apply material to a surface. This provides high transfer efficiency and lower overspray.


A hybrid vehicle is a vehicle that uses two or more power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors.

Hybrid vehicle

Vehicles that use both a traditional engine (combustion) and a rechargeable system (typically operated by a battery) to improve mileage, cause less pollution, and decrease need for fossil fuel.


A system for transmitting and modifying force by the use of a liquid. Consists of a pump, control devices, hydraulic lines and slave cylinders.

Hydraulic Brake

Brake actuated only by hydraulic pressure.

Hydraulic Clutch

A clutch, operated by fluid pressure.

Hydraulic Hoses

Hoses that carry fluid under high pressure.

Hydraulic Lifters

Hydraulic cam followers in the valve opening mechanism.

Hydraulic Pedestal

Self-adjusting support for a finger tappet in the valve opening mechanism.

Hydraulic Pressure

Pressure applied by a fluid.

Hydraulic Tappets

Self-adjusting cam followers in valve opening mechanism.

Hydraulic Valves

Valves used to control pressure or flow of a hydraulic fluid.


A compound which contains only carbon and hydrogen, which are distillate by-products of petroleum, natural gas and coal.

Hydrocarbon (HC)

Chemical compound which contains only, or principally, Carbon and Hydrogen. The principal constituent of liquid fossil fuels.

Hydrocarbon Emissions

Fuel vapours released into the atmosphere from a vehicle exhaust or fuel tank.


To break down (a hydrocarbon) by the process of hydrocracking. This is a catalytic cracking process of breaking down large hydrocarbon molecules into smaller ones


Reaction with water. Usually refers to a decomposition process leading to paint failure.


Instrument used for measuring specific gravity/relative density of a liquid (coolant, battery electrolyte).

Hydropneumatic Suspension

A suspension system using a liquid to transfer suspension movements to pneumatic (gas) springs.


Instrument used for measuring relative humidity - in an automotive context it is used to check moisture content of brake fluid.


A paint film or other solid that readily absorbs water.

Hypoid Gearing

Bevel gear with the axes of the driving and driven shafts at right angles, but not in the same plane, giving some sliding action between teeth. Widely used in rear axle final drives.


A characteristic of materials, sensors and sometimes instruments to make their behaviour dependent on the immediate history to which they have been subjected. Typically the final settling point is different when approached from above to when it is approached from below

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