Flat Washer, Flat Washer Type Standard, Dimensional Standards AMPG 2001 FL.01, Material Steel, Material Grade/Class Case Hardened, Finish Black Oxide, For Screw Size 1/4 in, Inside Diameter 0.281 in, Outside Diameter 5/8 in, Maximum Thickness 3/16 in, System of Measurement Inch, Minimum Thickness 3/16 in, Color Black, Inside Diameter Tolerance +/-0.010 in, Material Quality Standards ASTM A108, Outside Diameter Tolerance +/-0.010 in, Pack Size Small Pack, Rockwell Hardness C4