The Profile Spline Drive sprocket is manufactured from 7075 Aluminium in the USA. This sprocket requires no sprocket bolt, instead it has a hardened CrMo steel insert in that matches up to the 48 splines in your Profile BB spindle. (These can be used with all 19mm 48s spline cranks but we have some specific no boss Profile Cranks in 175mm Black only available for a clean look and lighter set up - see the bottom of this page).