Dophee 2Pcs Diamond Holesaw Hole Saw Tile Ceramic Glass Porcelain Marble Drill Bits (18mm) Usage: Excellent for making clean and accurate hole on glass, plastic plate and plank. It can cut tidy, smooth, no broken edges and no tremor phenomenon. Small incision resistance, improve the aperture rate. Easy to decorate after grooving, and easily remove the debris. Can be used with a electric drill,bench drill,high power grinder, pneumatic drill, magnet drill. Always use lubrication (water), otherwise the diamond core drill will burn. Size: Coated Core Drill Diameter 18mm