Diameter: 13mmDiameter 2: 20mmThickness: 3mmMaterial: SteelFinish: ZincHardness: Class 8Type: Flat WasherSpecifications: SAEA 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.