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AARAbbreviation for “American Association of Railroads”

Absolute viscosityA term used interchangeably with viscosity to distinguish it from kinematic viscosity or commercial viscosity. It is occasionally referred to as dynamic viscosity.

AcidityIn lubricants, acidity denotes the presence of acid-type constituents whose concentration is usually defined in terms of acid number. The constituents vary in nature and may or may not markedly influence the behavior of the lubricant. (See also Acid Number)

Acid Number See Strong Acid Number and Total Acid Number

Additive A chemical compound or compounds added to a lubricant for the purpose of imparting new properties or to improve those properties that the lubricant already has.

AGMA Abbreviation for “American Gear Manufacturers Association,” an organization serving the gear industry.

Aniline Point The Aniline Point of a petroleum product is the lowest temperature at which it is completely miscible with an equal volume of freshly distilled aniline.

Anti-Friction Bearing A rolling contact type bearing in which the rotating or moving member is supported or guided by means of ball or roller elements. Does not mean without friction.

Antioxidant A substance which retards the action of oxidation.

API Gravity A gravity scale established by the API and in general use in the petroleum industry, the unity being called the “API degree.” This unit is defined in terms of specific gravity as follows:

Sp.gr. (@60°F) =             141.5             
(Degrees API + 131.5)

Degrees API = [141.5 / sp.gr.(60°F)] – 131.5

Apparent viscosityA measure of the resistance to flow of a grease whose viscosity varies with shear rate. It is defined by the ratio of the shear stress to the shear rate calculated from Poiseulle’s equation at a given rate of shear and is expressed in poises.

Asphaltic Essentially composed of or similar to asphalt. Frequently applied to naphthenic base lubricating oils derived from crudes that contain asphalt.

ASTM Abbreviation for “American Society for Testing Materials,” a society for developing standards for materials and test methods.

Axial Load Bearing A bearing in which the load acts in the direction of the axis of rotation.

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