Spherical Washer Bottom Washer Inside Diameter 0.313 in Bottom Washer Outside Diameter 0.625 in Bottom Washer Radius 0.75 in Finish Black Oxide For Screw Size 1/4 in Material Steel Maximum Thickness 0.188 in Minimum Thickness 0.188 in Pack Size Small Pack Rockwell Hardness C40 Spherical Washer Type Spherical Washer Assembly System of Measurement Inch Top Washer Inside Diameter 0.281 in Top Washer Outside Diameter 0.625 in 1 Pair