washer

(design engineering) A flattened, ring-shaped device used to improve the tightness of a screw fastener.
(engineering) A device for removing dirt and soluble impurities from pulp and paper stock. A system for washing photographic materials to remove soluble products of developing or fixing. A power-driven machine for washing clothes and household linens. Also known as washing machine. scrubber

A flattened, ring-shaped device used to improve the tightness of a screw fastener. Three types of washer are in common use: plain, spring-lock, and antiturn (tooth-lock washers). Standard plain washers are used to protect a part from damage or to provide for a wider distribution of the load. Because a plain washer will not prevent a nut from turning, a locking-type washer should be used to prevent a bolt or nut from loosening under vibration (see illustration). Lock washers create a continuous pressure between the parts and the fastener. The antitum-type washers may be externally serrated, internally serrated, or both. The bent teeth bite into the bearing surface to prevent the nut from turning and the fastening from loosening under vibration. See also Screw fastener.

Lock washers. (After W. J. Luzadder, Fundamentals of Engineering Drawing, 6th ed., Prentice-Hall, 1971)