- H -

Head Gasket

A gasket that is used to enhance sealing between a cylinder head and an exhaust manifold or header.

Head Light Lens

See headlight lens.

Head Liner

See headliner.

Head Pressure

Pressure of the refrigerant from the discharge valve through the lines and condenser to the metering-device inlet.

Head Unit

The in-dash part of an audio system that includes a radio receiver/tuner and possibly a cassette tape or CD player. Some original equipment head units can be used to control a CD changer. A typical audio system upgrade is a "head plus four," meaning a new head unit and four new speakers.

Head-gasket Notch

A series of one to four notches used to measure the thickness of a gasket to control the piston-to-head clearance on a diesel engine.

Head-land Ring

A top compression ring with an L-shaped cross section.

Head-saver Shims

Shims that are used to compensate for material removed during head resurfacing to maintain correct overhead-cam drive-chain tension.

Headache Rack

A rack that is provided at the rear of a truck-cab interior to prevent a load from crashing through the rear window.

Headache Rack

A metal guard that mounts to a pickup truck's bed behind the cab and prevents cargo from crashing through the rear window. Also called a cab guard. Some models are more for style than for protection. Some cover the top brake light on the rear of the truck cab, so these models typically include a built-in brake light which will need to be wired. Many headache racks are available with mounting systems for auxiliary lighting.

Header

1. A vehicle crash. 2. A free-flowing exhaust manifold used on high-performance cars.

Header

A high-performance exhaust manifold that often is made of steel or lighter-weight aluminum. Headers are designed to improve an engine's performance by allowing exhaust to flow more freely, or by "tuning" the exhaust to enhance performance during a specific engine rpm range. Some headers also have a "scavenging effect," which means they help pull exhaust gases out of the cylinder heads to improve performance. Many headers are available with a ceramic or other high-temperature coating.

Header Tank

The top and bottom tanks or side tanks of a radiator in which coolant accumulates or is received.

Headlamps

The lights at the front of a vehicle used to illuminate the road ahead. Also known as headlights.

Headlight Cover

A restyling product that typically snaps on over a headlight to change its color or shape. Adding a set of headlight covers is a quick, easy and inexpensive way to change the look of a vehicle. Some headlight covers are made of black plastic for a blackout look.

Headlight Delay

A system that turns off the headlamps automatically after the operator leaves the vehicle, though the lights were left on.

Headlight Lens

The plastic (or, on vintage vehicles, glass) covering over a headlight. Specialty lenses are available in several colors, so consumers can change the look of a vehicle's headlights, taillights, turn signals and side marker lights.

Headlight Mask

A vinyl decal that can be cut to virtually any design and applied over a vehicle's headlights for a restyling effect.

Headlight Protector

A wire covering that attaches over a pickup, van or SUV's headlights, often as part of a larger tubular grille guard, to protect the headlight lenses from brush in off-road applications or to provide a tough, urban warrior look on the street. Headlight protectors typically can be removed quickly and easily to change a light bulb. Most companies offer matching taillight protectors.

Headlights

A term used for headlamps.