Inner Diameter (mm): 31 Washer Type: Flat Outside Diameter (mm): 22 Inside Diameter (mm): 10.5 Outer Diameter (mm): 57 Thickness (mm): 2.5 Fits Bolt Sizes (mm): M30 Coating: Zinc Phosphate + Oil offers corrosion protection up to the point of assembly (recommend painting for external applications). Salt spray resistance of 72 hours to red rust. Coating color - dark grey to black. Material: Hardened Steel Material Description: Hardened Steel