This is a special metric size bolt for holding the original Metro type 4 pot caliper to the hub but with UNF thread to fit the mini swivel hub. This special bolt stops any movement of the hub under braking that was encountered by the standard caliper bolt 53K1048. 3/8" unf thread 1.375"long, the shank is 9.8mm wide whereas the 53K1048 is 9.4mm. These do not fit the C-AJJ4023 alloy calipers.