Feature: 1. 100% brand new and high quality! 2. Diamond coated core drill bit removes a complete circle from glass, tiles, marble, granite, ceramic or other. Can be used with a standard electric drill. 3. Easy to use: Start your hole diagonally, make a round trace and then hold drill straight. 4. Warning: They should be use lubrication (water), Otherwise the diamond core drill will be burned. 5. Size(Diameter): 8mm, 10mm, 12mm, 14mm, 16mm, 18mm,20mm, 22mm, 25mm,50mm OR 6mm Usage： 1. Clean the surface and keep it wet with water& coolant.Then mark down the position of the drill hole. 2. Start drilling with a 45 degrees angle to the surface slowly. 3. Drill at low speed and adjust the drilling angle to vertical position when the hole appears. 4. Slown down to drill the hole off directly or you can exit and drill from the other side to make it smoothly.