0steel mil-s-7420; rockwell c scale 58 to 62 hardness; 0.396 in. Od; 0.232 in. Id; 0.099 in. Thk; one side 0.284 in. Diameter recess; 0.048 in. Depth of recess; two lugs 180 degrees apart on recess side of item 0.062 in. Lg of lug; 0.092 in. W of lug