Countersunk Washer Material Grade/Class Not Graded Material Steel Finish Black Oxide For Screw Size M4 Maximum Inside Diameter 4.3 mm Outside Diameter 20 mm Countersink Angle 90 Degrees Overall Height 3 mm System of Measurement Metric Color Black For Use With Flat and Oval Head Screws Industry Standards AMPG 2002 FIN.31 Pack Size Small Pack Rockwell Hardness C40 Thickness Tolerance +/-0.3 mm Package Quantity 5