3M Ninja Premium Diamond Grinding disc accurately sharpens high speed and carbide tooling, drills, chisels and gravers. discs also can be used to grind gemstones, smooth out chips and remove heavy or fine scratches on watch crystals. Abrasive can be used wet (recommended) or dry. For high polish, follow with the premium diamond polishing pack. The discs have peel-and-stick backs for sticking to the Ninja Cushion or Jooltool backpads. Use wet at slow speeds. Includes one 220 grit diamond disc. For use with Jooltool.