Flat Washers, Plain Washers


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FLAT OR PLAIN WASHERS


Flat Washer	Fender Washer	Beveled Washer	7/16 SAE yellow flat washer over 7/16 USS silver flat washer

Flat washers, also sometimes called plain washers, are used under bolt heads or nuts to increase the bearing area or offer greater hardness, so that the nut or bolt can be rotated without distortion of the bearing surface. Flat washers are also used to give tightness to a joint, to prevent leakage, and especially to distribute pressure under the head of a nut or bolt.

There are two common flat washer styles, based on the evolution of this part: USS (United States Standard) flat washers and SAE flat washers (originally approved by Society of Automotive Engineers). USS flat washers have a larger outer diameter than SAE flat washers. Differences between USS and SAE flat washers are reflected in each item's actual physical measurements; unless the buyer has a specific USS or SAE requirement, the buyer should consider the measurements, based on need, and not whether the flat washer is USS or SAE.

In addition, Fender flat washers have a large outside diameter in comparison with the inside diameter (hollow section). Malleable flat washers are made from cast iron or galvanized iron. The Beveled flat washer offers a square outer diameter, and is generally thicker than USS or SAE flat washers.