Square Washer, Dimensional Standards AMPG 2017 SQ.01, Material Steel, Material Grade/Class Case Hardened, Finish Black Oxide, For Screw Size M30, Inside Diameter 38 mm, Outside Diameter Not Applicable, Maximum Thickness 6 mm, System of Measurement Metric, Minimum Thickness 6 mm, Color Black, Made in North America Made in North America, Material Quality Standards ASTM A108