The wheels of different shapes are coated with diamond or CBN abrasive more or less concentrated in relation to the material and the operation to be done. The diamond wheels are suitable for hard metals, cermets, fiberglass, graphite, oxide ceramic materials, glass, ferrite, refractory materials, porcelain, kevlar, etc. CBN (cubic boron nitride) wheels are for high speed steels, case hardening steels, chromium steel and cast irons. The particle size is classified according to FEPA standards. The concentration must be chosen in relation to the process to be done.