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Glossary of Terms - All Terms

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Glossary Subsets


A type of measure having its zero point (base point) as being the complete absence of the entity being measured.


The Annular Bearing Engineering Committee. Also used with a number from 1 - 9 for tolerance grades (precision) of bearings. ABEC1 is standard, ABEC9 is ultra-precision.

Absolute Pressure (PSIA)

The pressure above zero absolute, the sum of both atmospheric and gage pressure.


Acrylonitrile Butadiene Styrene. A thermoplastic polymer that has moderate resistance to heat, low temperatures and chemicals. ABS also bonds to many different adhesive materials.


A container in which fluid is stored under pressure as a source of fluid power. The accumulator also absorbs shocks and smoothes out an operation.


Acetal resins are high performance engineering plastics with superior abrasion resistance and toughness. These resins may require pretreatments to enhance adhesion properties.


A chemical that speeds the curing of an adhesive. It is added in a minor quantity compared with the amounts of the primary reactants. Also referred to as a catalyst.


A device used to convert hydraulic energy into mechanical energy. A device to convert rotary motion into thrust or linear motion.

Adapter Assembly

An assembly for locking a tapered bore bearing to a shaft. The assembly consists of an adapter sleeve, locknut and lockwasher.


Anti-Friction Bearing Manufacturers Association. This group sets standards for the bearing industry.


American Gear Manufacturers Association. One activity of AGMA is the establishment of standards for gear lubricants.


A compound that enhances some property of, or adds a new property to the base fluid. Some types of additives include anti-oxidants, anti-wear additives and corrosion inhibitors to list a few.


The presence of air in the hydraulic fluid. Excessive aeration causes the fluid to appear milky and also causes components to operate erratically. This is because of compressed air trapped in the fluid.

Air Gap

The gap between the rotor and stator in an electric motor.

Aircraft Bearing

A term generally applied to bearings used by the aircraft industry or the Air Force. These bearings usually have to meet some Military Specification for quality and performance.

Airframe Bearing

A bearing designed for use in the control systems and surfaces of an aircraft.

Alternating Current (AC)

Electric power supplied in single or three-phase forms. In the United States, 60 Hz is the standard, while overseas, 50 Hz is the standard. AC current cycles or changes its direction of flow.


A condition where the center lines of two shafts are in line (coaxial).

Ambient Temperature

The temperature of the surrounding environment, usually air, in which the system components operate.

Amp Meter

Used to read amperage in individual lines.


A unit of electric current flow. One ampere will flow when one volt is applied across a resistance of one ohm.


The measurement of the flow of the electrical current.


The height of a waveform above ground, equivalent to 1/2 peak-peak value.

Angular Contact Bearing

A bearing in which the design creates a contact angle between the inner race, outer race and rolling element when the bearing is in use. Because of the design, angular contact bearings support both axial and thrust loads.

Annular Area

A ring shaped area that often refers to the effective area of the rod side of a cylinder piston, that is, the piston area minus the rod area.

Amplitude of Sound

The loudness of a sound.

Annular Bearing

A rolling element bearing designed primarily to support a load perpendicular to the shaft axis. Commonly referred to as a radial bearing.

Anti-Friction Bearing

A term commonly used for a rolling element bearing, such as a ball or roller bearing.

Anti-Wear Agent

An additive that minimizes wear caused by metal-to-metal contact.


American Petroleum Institute. The society formed to further the interests of the petroleum industry. One of the API's activities has been the development of the API Service Classification for gearcase oils.


Related to or based on water containing compositions.


The rotating member of an electric motor. In brush-type DC motors, the armature consists of the main current carrying windings (conductors) in the rotor. The commutator switches the power supply to the armature windings to generate a magnetic field.

Armature Current

The rated armature circuit current when the motor is operating at full load.

Ash Content

The non-combustible residue of a lubricating oil. Since some detergents contain metallic compounds, the percentage of ash has been considered to have a relationship to detergency.


American Society of Lubrication Engineers. The prior name of an organization involved with friction, wear, and lubrication. They are now known as the Society of Tribologists and Lubrication Engineers (STLE).

Atmosphere (ONE)

A pressure measure equal to 14.7 psi.


The American Society for Testing and Materials, an organization devoted to the promotion of knowledge of engineering materials and the standardization of specifications and methods of testing.


The decrease in signal amplitude during its transmission from one point to another.

Auxiliary Contacts

Contacts of a switching device in addition to the main current contacts. These contacts can be normally open or normally closed and alternate their state when operated.

Atmospheric Pressure

Pressure on all objects in the atmosphere because of the weight of the surrounding air. At sea level, this is about 14.7 pounds per square inch.


In the same direction as the axis of the shaft.

Axial Internal Clearance

Also referred to as end play, it refers to the maximum movement possible of the outer race relative to the inner race.

Axial Load

A load that is parallel to the axis of the shaft, also referred to as thrust load.


An imaginary line running through the center of a shaft, also referred to as center line.