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Heliarc Welding

The act of electrically joining two pieces of aluminum or stainless steel using a high-frequency electric weld and an inert gas, such as argon, that is fed around the weld to prevent oxidation.

Helical

A device, such as a spring, shaped like a helix or spiral.

Helical Compression Spring

An open-pitch spring, in a variety of configurations, used to resist applied compression forces.

Helical Extension Spring

A spring, usually made of round wire, that exerts a pulling force with various types of end hooks or loops by which they are attached to the load.

Helical Gear

A gear having teeth cut at an angle across its face, or diagonally to the rotational axis.

Helical Spring

Springs made of bar stock or wire, coiled into a helical form, including compression, extension, and torsion springs.

Helmet

1. A device worn on the head to protect eyes, face, and neck from arc radiation, radiated heat, and spatter or other harmful matter expelled during arc welding, arc cutting, and thermal spraying. 2. Protective head gear.

Helmet

A head protector that a race car driver must wear in some series. Most helmets must undergo rigorous testing to receive safety certification, and many feature an expiration date. Full-face helmets completely cover a driver's face, while open designs leave all or part of the face exposed.

Helper Spring

An additional spring device that permits a greater load on an axle.

Helper Spring

A long, flat spring that gets positioned between a vehicle's stock rear leaf spring and its stock helper spring. It is designed to increase the vehicle's ride height and spring rate, for vehicles that occasionally carry a heavy load or tow, or that have been fitted with heavy accessories, such as a truck cap or winch. Helper springs also can allow you to install a taller wheel-and-tire combination.

Hemi

Half of a sphere.

Hemi Cammer

An engine having both hemispherical combustion chambers and an overhead camshaft.

Hemi Head

A cylinder head with hemispherical combustion chambers providing room for extra large valves or multi-valve arrangements and providing an ideal shape for smooth, even combustion.

Hemispherical Combustion Chamber

A type of combustion chamber that is shaped like half of a circle. This combustion chamber has the valves on either side with the spark plug in the center.

Henry

A unit of inductance. The inductance of a coil of wire in henries is a function of the coils size, the number of turns of wire and the type of core material used.

HEPA

An acronym for high-efficiency particulate air filter.

Heptane

A hydrocarbon that serves as a primary reference fuel with an index of 0.

Hermaphrodite Caliper

A combination tool having a caliper leg and a leg from a divider. Used in testing centered work and laying off distances from the edge of a piece or work.

Herringbone Gear

A gear cut in the V-shaped pattern of a small bony extension of a herring's spine.

Hertz

A unit of frequency of any regularly occurring event. Named for Heinrich Rudolf Hertz (1859 - 1894) a German physicist.