HELICAL--In the shape of a helix, which is the shape
GRID--A lead screen or plate to which battery plate
of a screw thread or coil spring.
material is attached.
HERRINGBONE GEARS--Gears having teeth
GROUND--(1) The point in an electrical circuit used
machined in a V-configuration.
as a common reference point for measuring
purposes. (2) To connect some point in an electrical
HIGH-SPEED CIRCUIT--In a carburetor, the pas-
circuit or some item of electrical equipment to earth
sages through which fuel flows when the throttle
or to the conducting medium used in lieu thereof, as
valve is fully opened.
in connecting an electrical unit to the engine or
HIGH TENSION--Another term for high voltage. In
frame to return the current to its source.
the electrical system, refers to the ignition
GUSSET PLATE--A plate at the joint of a frame
secondary circuit since this circuit produces
structure of steel to strengthen the joint.
high-voltage surges to cause sparking at the spark
HALON 1211--(A fire fighting agent) A colorless gas
with a faintly sweet smell. It will not conduct
HORN--An electrical signaling device on the vehicle.
HORSEPOWER--A measure of a definite amount
fires. The byproducts decompose at temperatures
above 900°F which leaves a sharp, irritating odor.
pound per second. To calculate horsepower:
HAND BRAKE--A brake operated by hand. Also
referred to as the parking brake.
HYDRAULIC BRAKES--A braking system that
HEAD--The height of a column or body of fluid above
uses a fluid to transmit hydraulic pressure from a
a given point expressed in linear units. Head is
master cylinder to wheel cylinders, which then
often used to indicate gauge pressure. Pressure is
cause brake shoe movement and braking action.
equal to the height times the density of the fluid.
HEAD, FRICTION--The head required to overcome
liquid pressure and flow.
the friction at the interior surface of a conductor
and between fluid particles in motion. It varies
HYDRAULIC VALVE TAPPET--A valve tappet
with flow, size, type, and condition of conductors
that, by means of hydraulic pressure, maintains
and fittings, and fluid characteristics.
zero valve clearance so that valve noise is reduced.
HEAD, STATIC--The height of a column or body of
fluid above a given point.
carbon found in vehicle emissions.
HEAD, VELOCITY--The equivalent head through
HYDROMETER--A device to determine the specific
which the liquid would have to fall to attain a given
gravity of a liquid. This indicates the freezing point
velocity. Mathematically it is equal to the square of
of the coolant in a cooling system or, as another
the velocity (in feet) divided by 64.4 feet per
example, the state of charge of a battery.
HYDROPNEUMATICS--Pertaining to the combina-
HEADLIGHT--Lights at the front of the vehicle
tion of hydraulic and pneumatic fluid power.
designed to illuminate the road ahead when the
HYDROSTATICS--Engineering science pertaining
vehicle is traveling forward.
to the energy of liquids at rest.
HEAT CROSSOVER--A passage from one exhaust
HYDROVAC BRAKES--A type of braking system
manifold under carburetor to the other manifold to
using vacuum to assist in brake operation. The
provide heat to the base of carburetor during
vacuum action reduces the effort required from the
driver to operate the vehicle brakes.
HEAT EXCHANGER--A device used to cool or heat
I-HEAD--A type of engine with valves in the cylinder
by transferring heat from one object to another.
HEAT STOVE--A metal shroud around the exhaust
IDLE--The engine speed when the accelerator pedal is
manifold or intake manifold that supplies the
fully released; generally assumed to mean when the
carburetor with warm air when needed.
engine is doing no work.