ICP (inductively coupled plasma): quantitative analytical technique for measuring metal contents of fluids.

Idler gear (gears): gear placed between two other gears to change a mechanism’s direction of rotation.

Inboard bearing (bearings): the bearing supporting a shaft nearest the coupling or drive mechanism.

Indicator (lube systems): device that shows movement of discharge piston.

Inhibitor: additive that prevents or retards undesired chemical changes, especially to metal surfaces; common inhibitors prevent oxidation, corrosion and rust.

Injector (lube systems): part that dispenses a measured amount of lubricant to a point of lubrication.

Injector body (lube systems): steel cylinder that serves as a container for lubricant passage, valve port, line connections and grease fitting assembly.

Inlet disc (lube systems): channel-lipped disc that directs lubricant through the valve port.

Inlet section (lube systems): top section of divider valve that contains the inlet connection, internal porting, tie rod holes and mounting holes.

Insolubles (oil): (ASTM D-893) a term used in the analysis of used oil, especially when determining the presence of oxidation products. The procedure dilutes the sample with pentane, causing the precipitation of oxidized material and other contaminants, collectively known as pentane insolubles. These insolubles are then treated with toluene to dissolve the oxidation products. The difference in weight between the pentane and toluene insolubles is called insoluble resins or oxidation products.

Insolubles (grease): (ASTM D-128) components of a lubricating grease that are insoluble in the prescribed reagents; generally denotes fillers, additives and certain types of thickeners as well as impurities.

Insulating oil/transformer oil: clean, dry, high-quality, oxidation-resistant oil of low viscosity and high dielectric strength, designed for extended service in circuit breakers, transformers, switches and other electrical apparatus; most commonly utilized for cooling in transformers.

Intensifier (hydraulics): device that converts low-pressure hydraulic or pneumatic power to high-pressure hydraulic power.

Interfacial tension (IFT): the energy per unit area existing at the boundary of two immiscible liquids, like water and oil; obtained by measuring the force required to rupture the interface. ASTM D-971 measures the force required to draw a platinum ring through the interface in dynes/cm. A lowered IFT promotes emulsification and indicates that oxidized products are forming in the oil.

Intermediate base crude: see mixed base crude.

Invert emulsion: water-in-oil emulsion, typically containing 40% water, utilized as a fire- resistant fluid; oil is the outer or continuous phase of an invert emulsion, in contrast to the normal (oil-in-water) emulsion, where water is the outer phase.

Involute tooth form: profile of a tooth face generated by unwinding a line from a base circle where the end of the line scribes the involute shape.

Iodine number: the amount of iodine absorbed by an oil under prescribed conditions; like the bromine number, it measures the percentage of unsaturates in an oil.

ISO: International Standards Organization

ISO viscosity classification system: internationally accepted system, in which each viscosity grade (VG) corresponds to the midpoint of the viscosity range expressed in centistokes at 40°C; originated with a Saybolt (SUS) system developed jointly by ASTM and STLE, later changed to centistokes to gain

international acceptance. The original Saybolt system rated viscosity at 100°F; the ISO system rates viscosity at 104° (40°C).