<p>MIDWEST FASTENER Flat Washer, 5/16 in ID, USS Grade, Stainless Steel, Package Quantity: 100.</p><p>A flat washer is a thin, usually round, plate with a hole in the middle that is normally used to distribute the load of a threaded fastener. USS flat washers have a large, wider body. SAE flat washers are machined to a tighter specification and have a smaller outside diameter.</p>