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
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.