The Profile Spline Drive sprocket is CNC machined from 7075 Aluminum in the USA with the same quality Profile is famed for. It requires no sprocket bolt. Instead, it has a hardened CrMo steel insert in that matches up to the 48    splines on the crank axle for pure, direct power transfer. Available for 19mm splined axles only. 1/8″ tooth width for use with most freestyle/street & single speed chains. Supplied with 19mm splined steel insert.