Diameter: 1/4Diameter 2: 9/16Thickness: 1/16Material: SteelFinish: ZincThread Type: USSHardness: Grade 2Nominal Size: 3/16Type: Flat WasherA 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.