Spherical Washer Bottom Washer Inside Diameter 0.688 in Bottom Washer Outside Diameter 1.375 in Bottom Washer Radius 1.75 in Finish Black Oxide For Screw Size 5/8 in Material Steel Maximum Thickness 0.313 in Minimum Thickness 0.313 in Pack Size Small Pack Rockwell Hardness C40 Spherical Washer Type Spherical Washer Assembly System of Measurement Inch Top Washer Inside Diameter 0.656 in Top Washer Outside Diameter 1.375 in 1 Pair