Flat Washer,M18 F/W 20 X 42 X 3.6-4.2 1, Dimensional Standards AMPG 2001 FL.01, Material Stainless Steel, Material Grade/Class Through Hardened, Finish Plain, For Screw Size M18, Inside Diameter 20 mm, Outside Diameter 42 mm, Maximum Thickness 4 mm, System of Measurement Metric, Minimum Thickness 3.6 mm, Inside Diameter Tolerance +/-0.010 in, Made in North America Made in North America, Material Quality Standards ASTM A564 Type 630, Outside Diameter Tolerance +/-0.010 in