Our 50BS21H sprockets are manufactured to conform to the ANSI standards for chain & sprockets. This sprocket is a 21 tooth sprocket that is compatible with ANSI #50 roller chain. The 50BS21 7/8" sprocket is a finished bore style that has a standard keyway & 2 setscrews. Our sprocket teeth are hardened to help prevent tooth wear. A black oxide finish is applied to the sprocket for corrosion resistance.