Zahn viscometer: a crude funnel viscosity device for factory and laboratory use, consisting of a wire bail that holds a cone-shaped cup with an orifice at the bottom. After the cup is filled with the sample, the test consists of recording the temperature and the time required for the test sample to flow from the filled cup. Cups with orifices of various sizes are available.

Zinc dialkyl dithiophosphate/zinc diaryl dithiophosphate/ZDDP: a popular anti-wear additive used in motor oils and hydraulic fluids; though it also has oxidation inhibiting properties, it cannot be used in engines employing silver bearings.

Zerk fitting: a common grease fitting, one of many types of fittings used in lubrication and hydraulics).

ZN/P curve: a graphic representation of the effects of speed (N), load (P) and viscosity on the coefficient of friction µ as a shaft rotates in a plain bearing. The dimensionless equation states that the coefficient of friction µ is a function (f) of the ratio (viscosity X speed)/load or µ = (f)ZN/P.