This replacement castle-style axle nut and cotter pin fit Straton Springers perfectly and are 5/8"-18 thread. Chrome plated. This castle nut could be used with other 5/8"-18 thread axles to add the safety of the cotter pin, ensuring the axle nut cannot loosen up. Straton Springer axles are already drilled for this purpose, other axles would need to be drilled to use the cotter pin.