Norton 38A toolroom wheels are manufactured using fast cutting White Aluminium Oxide. (White in colour). These wheels are designed to grind hardened tool steels.38A abrasive is more friable than brown aluminium oxide used in general purpose grinding wheels.Maintains cutting ability by self fracturing, as the grain fractures and breaks down new cutting points are exposed.This increased cutting ability also causes the wheel to wear faster than a general purpose grinding wheel.