428 Glossary of Terms and Abbreviations
Wicking: The vertical absorption of a liquid into a porous material by capillary
forces.
Work Penetration: The penetration of a sample of lubricating grease immediately
after it has been brought to 77°F (25°C) and then subjected to 60 strokes in
a standard grease worker (ASTM D217).
Worm Gear: A gear that is in the form of a screw. The screw thread engages the
teeth on a worm wheel. When rotated, the worm pulls or pushes the wheel,
causing rotation.
ZDDP: An antiwear additive found in many types of hydraulic and lubricating u-
ids. Zinc dialkyldithiophosphate.