A material which reduces friction by formation of an adsorbed film.

The OK load or the Timken OK load describes the load-carrying capacity of a lubricant. The OK load is measured in a standard test (ASTM D 2509). In this test, a bearing ring rotates against a stationary steel block under an applied load. The OK load is the maximum load that can be applied without scoring the steel block. It is used to characterize the extreme pressure performance of greases and lubricants. The name of this test refers to the Timken Company, which developed this machine.

An oleate is a salt or ester of oleic acid. Oleic acid is a fatty acid with chemical formula C₁₈H₃₄O₂ or CH₃-[CH₂]₇-CH=CH-[CH₂]₇-COOH. Oleate greases are made by reacting oleic acid with an inorganic base to form a salt, i.e., soap thickener.

The operating temperature of a grease is the range between the lowest temperature where a lubricated device can be started up in an acceptable manner and the highest temperature where lubrication is adequate. The operating temperature of a grease depends on its formulation (base fluid, thickener, additives). In this context, temperature is measured in the general vicinity of the lubricated contact and not between loaded surfaces. Low-temperature bearing or flow tests are used often to determine the minimum operating temperature. High-temperature bearing tests are used typically to determine the maximum operating temperature. Dropping point alone is not sufficient to determine the maximum operating temperature of a grease.

In general, organic acids are organic chemicals with acidic properties. Organic compounds contain primarily carbon (C) and hydrogen (H), and may contain smaller amounts of nitrogen (N), oxygen (O), sulfur (S), etc. Acidic molecules tend to release H atoms by reacting with basic molecules or dissociating in polar solvents. Many organic acids contain a -COOH or carboxyl group that can release an H atom.

An organic soap is an organic molecule that is formed by the chemical reaction of an acid and a base. Many grease thickeners are organic soaps formed by reactions of organic acids with inorganic bases. For example, grease can be prepared by reacting 12-hydroxystearic acid and lime (calcium hydroxide ) in base fluid to form calcium 12-hydroxystearate soap, which thickens the fluid to form grease.

See Non-Soap Thickener.

The resistance of lubricants to chemical reactions with oxygen. The absorption and reaction of oxygen may lead to degradation of lubricants. Several test methods are in use, including ASTM D942 (IP 142) and D5483.