Diameter: 7/16Diameter 2: 1Thickness: 5/64Material: SteelFinish: PlainThread Type: USSHardness: Grade 2Nominal Size: 3/8Type: Flat WasherBox of 336.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.