Flat Washer,M20 F/W 21 X 35 X 3.0-3.9 3, Dimensional Standards AMPG 2001 FL.01, Material Stainless Steel, Material Grade/Class 316, Finish Plain, For Screw Size M20, Inside Diameter 21 mm, Outside Diameter 4 mm, Maximum Thickness 3.5 mm, System of Measurement Metric, Minimum Thickness 3 mm, Inside Diameter Tolerance +/-0.010 in, Made in North America Made in North America, Material Quality Standards ASTM A276, Outside Diameter Tolerance +/-0.010 in