Diameter: 9/16Diameter 2: 1-3/8Thickness: 7/64Material: SteelFinish: Black ChromeThread Type: USSHardness: Grade 2Nominal Size: 1/2Type: Flat WasherBox of 5.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.