Saturday, 8 May 2021, 8:32 PM
Site: IMI eLearning
Course: IMI eLearning (IMI eLearning)
Glossary: Automotive Glossary


Simple connection device to allow a pressure gauge, for example, to be connected into a pipe or fuel line.




A meter for measuring the speed of rotation of a component or device. Used to describe the on and off vehicle instruments that measure engine speed.


The stickiness of a paint film or an adhesive. The time it takes for an air-drying paint to reach a tack-free state.

Tack Cloth or Rag

A cloth coated with a non-contaminating sticky substance used to remove dirt and lint prior to painting.

Tack Coat (grip coat)

The first sprayed coat of colour, applied lightly and allowed to flash-off only until it is quite sticky.

Tack-free Time

An indicator of a coating's hardness development. The surface of the film will not finger mark, yet the film is still not dry and hard throughout.

Tandem Master Cylinder

A brake master cylinder with two separate pumping chambers. Used for split circuit brake hydraulic systems.


A projection or lug used to hold or drive an attached part. Tang on a file to hold the handle.

Tank Sender

A unit in the fuel tank that indicates the fuel level.


A tool to cut internal threads. Cutting internal threads.

Tape Tracking

Markings left behind on a new paint film when masking tape was applied before it was hard enough to resist pressure marks.


Reducing in size along the axis of an object.

Taper Roller Bearing

A type of bearing consisting of a series of tapered or conical rollers held in a cage between inner and outer bearing tracks and able to carry thrust (axial) loads as well as radial loads.


A valve lifter or cam follower in the engine valve gear train.

Tapping Size

Thread core diameter, a drilling size.


Throttle Body


Throttle Body Injection.




Torque Converter Clutch


Transmission or Transaxle Control Module


Traction control solenoid (SAAB 9000)


Turbo Diesel


Top dead centre. The position of the crankshaft when the piston is at its highest position in the cylinder. The crankshaft is at 0° of rotation.


Turbo Direct Injection (A turbo charged direct injected diesel engine)


Time Division Multiple Access refers to a digital communication link where multiple devices share a single carrier frequency by taking turns. Each gets the channel exclusively for a certain time slice, and then gives it up while all the other phones take their turn.


Acting like a telescope in having a sleeved construction where one or more sleeves slide inside the outer sleeve. Modern shock absorbers and safety steering columns are generally of this type of construction.


A measure of the hotness or coldness of matter. The S.I. unit of temperature is the Kelvin (K) and is the same as minus two hundred and seventy-three degrees Celsius.

Temperature Differential

Difference in temperature between two components.


Baking of plastic parts to drive off internal mould release agents prior to painting.


Force due to a pulling effort.

Tension Rod

A trailing strut or rod positioned between the vehicle chassis and a suspension track control arm to hold it in position and to transmit driving and braking forces.


Opposing pulling forces (tension) that create a stress (tensile) in an object.


A device usually consisting of a small pulley to set belt tension.


Electrical connection points. Common types are described as spade, blade, ring and fork.

Test Cycle

Strictly controlled test procedure for exhaust emission evaluations.

Test Lamp

A simple bulb used for tracing circuit faults.

Test Port

A point where a test gauge may be connected.

Test Probe

A general term used to describe the device used to make contact when testing a circuit. The prods on the end of multimeter leads are good examples.

Test Rigs

Machines designed to allow components to be run and operated as if fitted to the vehicle. Used for test and calibration purposes.

Tetraethyl Lead

A petrol additive to reduce 'knock' or detonation. Also described as an octane enhancer.


Thick film ignition module.

Theoretical Coverage

Describes a paint's film thickness or hiding power. Defined as the number of square metres a coating should cover at a specified film thickness measured in microns.

Thermal Cycling

Laboratory testing of paint formulations by alternately heating and cooling a painted object to determine what effect this variation has on the paint's properties.

Thermal Efficiency

The ratio between the heat energy in the fuel and the power output from the engine.

Thermal Expansion

Increase in size of an object as temperature increases.

Thermal Gauge

Instrument gauges that use the heating effect of electricity to move a needle.


Resistor whose resistance is greatly reduced by heating.

Thermo Time Switch

A device containing a bimetal strip. It is used in conjunction with a cold start injector to deliver a set amount of extra fuel when starting from cold.


A device containing a bimetal strip. It is used in conjunction with a cold start injector to deliver a set amount of extra fuel when starting from cold.


A type of polymer paint or plastic which softens and melts when heated and then re-solidifies upon cooling. An example is 1K acrylic lacquer paint.


Temperature sensing valve controlling flow of coolant.

Thermostatic Control

A device that uses temperature for actuation.


Thermosyphon (or thermosiphon) refers to a method of passive heat exchange based on natural convection which circulates liquid without the necessity of a mechanical pump.

Thick Film Ignition Module

An integrated circuit ignition control module."


Solvent added to a paint to reduce its viscosity to a sprayable consistency.

Third Party

Another party, not one's self (legal).

Thread Pitch

Distance from the top or peak of one thread to the top of the next.

Threaded Unions

Usually pipe connections using threaded connections.

Three Phase Electric Current

The internal alternating current output from an alternator stator and made up from three single phases starting at 120 degree intervals. The three phases are rectified to a direct current output for charging the battery and supplying the vehicle electrical systems.

Three Point Seat Belt

Type of seat belt that has a single belt threaded across the lap and shoulder and anchored at three points. The anchorage points are both sides of the lap and on the pillar above the shoulder of the wearer. Also known as a lap and diagonal belt.

Three Point Static

Type of seat belt with lap and diagonal webbing.

Three Quarter Floating Axle

An axle hub arrangement with one bearing mounted in a hub on the axle casing. Although the load is carried mainly by the hub there are shear and bending forces applied to the axle shaft.

Three Way Converter

A dual bed catalytic converter with one stage coated with platinum and palladium and the other with platinum and rhodium. Converts HC (Hydrocarbons) and CO (Carbon Monoxide) to H (Hydrogen) and CO2 (Carbon Dioxide); and NOX (Nitrogen Oxides) to N (Nitrogen) and O (Oxygen).

Three-lobe Cam

A triangular shape cam.


The engine speed control mechanism operated by the driver.

Throttle Body

A simple unit containing a throttle butterfly. Use as part of an injection system.

Throttle Body Injection

A petrol fuel injection system using a single point injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also single point injection (SPI).

Throttle Butterfly

The restrictor (plate) in the air intake of petrol injection ducts or carburettors.

Throttle Plate

The restrictor (butterfly) in the air intake of petrol injection ducts or carburettors.

Throttle Position Sensor

Sensor for throttle position information to engine management system.

Throttle Potentiometer

A variable resistor that is moved with the throttle to allow position of the throttle to be sensed.

Throttle Pressure

Shift control pressure in an automatic transmission regulated by engine speed and load conditions.

Throttle Spindle

The shaft on which the throttle butterfly moves.

Throttle Switch

A switch that operates when the throttle is fully open or fully closed.

Throttle Valve

A valve in an automatic transmission that responds to throttle position or inlet manifold vacuum to regulate the throttle pressure.


The engine speed control mechanism operated by the driver.

Throttling Bore

A fixed size orifice used to control or restrict flow.

Through- Cure

The completion of the curing process at which no further chemical reaction can occur to aid in film formation.


The dimension from the centre axis of the crankshaft to the centre axis of the big end bearings.


Force acting on an object causing it to change position or alignment with another object. Also used to describe a force along an axis where two components are forced together.

Thrust Bearing

Bearing intended principally to react to axial or thrust loads. Thrust race (Informal).

Thrust Face (Piston)

The side of a piston pressed against the cylinder wall during the combustion stroke. The opposite side to the connecting rod direction of travel.

Thrust Plate

A plate that applies thrust (force).

Thrust Plates

Plates used to apply thrust (pushing force) to another component.


A silicon controlled rectifier used as a switching device using a very low control current to switch much larger currents. Thyristors are switched on by a gate control current and remain on until the main current flow ceases.

Tick Over

Rotational speed of an engine on no-load and minimum throttle setting. Also idle or curb idle.

Tie Rod

A connecting rod in a steering system between the drop arm (Pitman arm), the idler arm and the steering arms on the steering swivels.

Time Lag

A delay in operation.


Reference to the time that information was recorded.


Relative crankshaft rotational points of action within the engine operating cycle particularly for ignition and valve opening.

Timing Belt

A toothed drive belt that droves from the crankshaft pulley to the camshaft. In some cases the drive is also to an ignition distributor or diesel injection pump.

Timing Chain

Chain that drives the camshaft from the crankshaft.

Timing Marks

Marks on the crankshaft pulley, flywheel, distributor drive pulley and/or camshaft pulley. Used to accurately time and an engine.


An individual pigment from a family of pigments used on a mixing machine to produce a colour match to the vehicle to be painted. Also refers to the act of colour adjustment where small amounts of tinters are added to mixed colour to correct a mismatch

Tinting Strength

The ability of a pigment to change the colour of a paint to which it is added. Some pigments have high tinting strength and only a small amount is necessary to make a large change in colour.


Tires (or 'tyres' in British English) are ring-shaped parts, either pneumatic or solid, that fit around wheels to protect them and enhance their function.

Titanium Dioxide

A non-toxic, non-reactive, white pigment. Has the greatest hiding power of all white pigments.


Thermactor Idle Vacuum Valve


Throttle Kicker Solenoid

Toe (Wheel Alignment)

The relative angle of the road wheels to the true longitudinal axis of the vehicle. The toe angle is the degree of variation needed to bring the wheels into true rolling motion when the vehicle is travelling.

Toe In

Basic setting of the road wheels on one axle when adjusted so that the front edges are angled very slightly inwards. Free play in the steering gear or suspension arms is taken up during forward motion to bring the wheels to a parallel position.

Toe Out

Basic setting of the road wheels on one axle when adjusted so that the front edges are angled very slightly outwards. Free play in the steering gear or suspension arms is taken up during forward motion to bring the wheels to a parallel position.

Toe Out On Turns

The difference between the angles of turn of the steered wheels when cornering. The angles are measured at 20 degrees for the inner wheel when checks and comparisons are being made. The outer wheel angle should be less than the inner wheel.


The amount that any dimension can be from the nominal size.


A widely used solvent or diluent or a co-solvent. (Co-solvents are used to help make sure the paint forms a tough, durable film). A fast-evaporating, high solvency, aromatic hydrocarbon.

Tone Disc

A metal disc that sets the tone (frequency and volume) at which a horn operates.

Top Coat

The final layer of paint applied to a substrate. Several coats of topcoat may be applied in some cases.

Top Dead Centre

The position of the crankshaft when the piston is at its highest position in the cylinder. The crankshaft is at 0° of rotation.


Paint for appearance and weather seal.

Topping Off

Topping up.

Topping Up

Process of making sure a fluid is full to the top or appropriate level marking.


Rotary or turning force. The SI unit of torque is Nm. The force in Newtons multiplied by the distance in metres.

Torque Converter

A fluid flywheel with a stator that creates a back force in the turbine that is added to the force from the impellor to give an increase in output torque.

Torque Settings

Values recommended by a manufacturer, to which certain fixings should be tightened.

Torque Wrench

A calibrated wrench that allows tightening and adjustment of fasteners to a specified torque setting.


Type of bolt used for holding cylinder heads. They are made from a steel alloy that allows a tough hold down force at the yield point of the material. These bolts usually require tightening by an angular value and replacement whenever they are removed.


A twisting force that results in torsional stress.

Torsion Bar

Metal spring used in vehicle suspension. Uses a twisting action along the length of the spring to provide suspension movement.

Torsion Springs

A spring that works by twisting.

Torsional Strength

Ability to withstand rotational force.

Torsional Stress

The stress that occurs when twisting forces are applied.


Trade name for a hexagonal/star shaped tool that has extra machined slots for a better grip.

Total Displacement

Applied to the sum total of the swept volumes for all cylinders in an engine. Also known as 'engine capacity'.


Correcting minor scratches, stone chips, etc., usually by the use of a small brush.

Toughened Glass

Soft glass with tough outer skin produced by heat treatment tempering.

Towing Socket

A multisocket used to make electrical connections to a trailer.


Throttle Plate.


Tuned Port Injection


Throttle Position Potentiometer


Throttle Position Sensor.


Throttle Position Transducer

Track (Wheel)

The dimension between the centres of the road wheels on one axle. Also known as tread.

Track Arm (Track Control Arm)

A transverse lower suspension arm attached to the chassis at the inner end and to a McPherson strut at the outer end. Maintains the wheel track position and transmits transverse forces.

Track Rod

Transverse rod that connects the steering arms of steered wheels and so maintains the geometric relationship between them when steering.

Track Rod End

A ball joint coupling on steering track rod ends that join the track rod to another component to allow a range of angular movement.


In electrical terms it is the loss of an electrical current outside of an insulator. The term is also used to describe the setting procedure for adjusting front wheel steering alignment.


The grip of the tyre with the road surface. The 'grip' can be specified as a coefficient of friction where the higher the number the greater the ability to transfer a force. (1 represents 100% for all force loads, tyres are generally in the range 0.75 to 0.85).

Tractive Effort

The forward force of a vehicle while it maintains tyre contact with the road surface.

Trailing Arm

A suspension link or rod that carries an axle behind the mounting and pivoting point of the arm. Semi trailing arms are mounted at angle to the longitudinal and transverse axes of the vehicle.

Trailing Edge

The back edge of a brake shoe in relation to the direction of rotation of the brake drum.

Trailing Shoe

A brake shoe that has a trailing edge making first contact when applied.


(1) Rear axle assembly that incorporates the main change-speed gearbox. (2) Combined gearbox and final drive unit attached to the engine in some front wheel vehicles. Contraction of transmission-axle.

Transaxle Gearbox

(1) Rear axle assembly that incorporates the main change-speed gearbox. (2) Combined gearbox and final drive unit attached to the engine in some front wheel vehicles. Contraction of transmission-axle.


An electronic device that converts a minute amount of one form of energy to another. A moving wheel with a tooth pattern can induce a voltage in a coil of wire around a magnet. This arrangement is used for speed and position sensors. Other transducers are used for other sensor applications.

Transfer Box

The gearbox that splits drive front and rear for four wheel drive transmissions.

Transfer Box/Case

The take-off gearbox for four wheel drive transmissions.

Transfer Efficiency

The measure of paint material applied compared to the amount of material originally sprayed. Modern HVLP spray guns are expected to achieve a transfer efficiency of at least 65%

Transfer Port

The port that connects the crankcase to the cylinder on a two stroke engine and is used to pass a new air/fuel charge to the cylinder when the piston descends to bdc.


Two coils or windings that interact to step voltage up or down.


Semi-conductor devices with three electrodes. Electronic switches and amplifiers.

Transition Fit

The relationship between the dimensions of two components where one fits inside the other. In this instance the fit is one where the inner dimension of the outer component is the same as the outer dimension of the inner component. Also known as a push fit.


Allowing light, but not detail to pass through. Semi-opaque


(1) (US: gearbox) Mechanical unit containing a manual or automatic change speed gear system and associated actuating machinery. (2) (UK) Collective term for the components, such as clutch, gearbox, drive shaft, whereby power is transmitted from engine to driven wheels (mainly UK usage).

Transmission Fluid

The oil used in a transmission system - several types are used so always check data.

Transmission Ratio

Usually used to describe the overall ratio of the transmission - from the engine to the wheels.


Device that outputs a signal, usually a radio signal (TV or radio transmitter) but in some cases wires are used (temperature transmitter for example).


Clear/clarity; Allowing light and detail to pass through; Not opaque.


Any axis running across a vehicle or other object at right angles to the longitudinal axis.

Transverse Axis

Any axis running across a vehicle and parallel with the ground and at right angles to the longitudinal axis of the vehicle.

Transverse Engine

An engine fitted across the axis of a motor vehicle.


A trapezoid (in North America) or trapezium (in Britain and elsewhere) is a quadrilateral two of whose sides are parallel to each other. Some authors define it as a quadrilateral having exactly one pair of parallel sides, so as to exclude parallelograms. It is the shape made by the linkages in an Ackerman steering system.

Tread (Tire)

The surface of a tire that contacts the road surface and is cut to aid traction and dispel moisture.

Tread (Tyre)

The surface of a tyre that contacts the road surface and is cut to aid traction and dispel moisture.

Tread (Wheel)

The dimension between the centres of the road wheels on one axle. Also known as track.


A switch that is operated by movement of a vehicle. Used in alarm system.


A basecoat, followed by a transparent or translucent mid-coat, followed by clearcoat; to provide a special colour effect on the vehicle.

Tri-pod (Tri-pot) Joint

A constant velocity joint consisting of three drive pins and balls set in three axial tracks.

Trickle Charge

A very slow charge rate for a battery. Usually 1 or 2A overnight.

Trim Height

A measurement taken from a fixed point on the vehicle body to the centre of the wheel.

Trip Computer

A computer built in to some vehicles. It allows the display of different values such as average fuel consumption and estimated time of arrival at a destination.


A pivoting assembly consisting of a rod and bearings.


General name for large pipes or tubes usually used to carry air.


Throttle Solenoid Positioner

Tuned Intake Pressure Charging

A system of intake air management that maximizes the flow of air into an engine by using the reciprocating air resonance in the manifold at different engine speeds.


Steel grey heavy metallic element with very high melting point. Used for light bulb filaments.


The driven member in a turbocharger, turbine engine and torque converter. The turbine consists of a set of blades on a central boss and shaft and is driven by exhaust gases in a turbocharger or turbine engine and by liquid from the impeller in a torque converter.


Engine with a turbocharger, which is an exhaust driven device that pumps in extra air.


Air supply pressure charger driven by the engine's exhaust gas flow.

Turn angle sensor

A device that measures and outputs a signal proportional to the angle that a vehicle is turning.

Turning Centre

An imaginary point about which a vehicle turns when cornering. Also known as the instantaneous centre of turn or rotation.

Turning Circle/Radius

The minimum circle or radius in which a vehicle can turn when on full steering lock.


Throttle Valve


Thermal Vacuum Switch


Three way catalyst.


Three Way + Oxidation Catalytic Converter

Twin Choke Carburettor

A carburettor with two venturis either acting together or progressively.

Two Stroke Cycle

An engine operating on two strokes of the piston. Induction occurs in the crankcase below the piston on the upstroke and is transferred to the cylinder at the end of the down stroke. Compression takes place above the piston on up stroke. The combustion and exhaust strokes occur above the piston on the down stroke.

Two-component System (2K)

Materials such as paints, fillers, and adhesives which require the addition of a hardener or activator to accomplish a chemical reaction, causing them to cure.


Two different colours on a single paint job.


Tyres (or 'tires' in American English) are ring-shaped parts, either pneumatic or solid, that fit around wheels to protect them and enhance their function.