It has two big kind: Browm Aluminum oxide with glass fiber backing or Resin fiber backing, Zirconium Aluminum oxide with glass fiber backing or Resin fiber backing. It has kinds of specifications, including different diameters(100mm, 115mm, 125mm, 125mm, 150mm, 180mm) , layers(6-10layers) , etc. Usage: It can be applied to grinding kinds of steel, cast, wood, etc.