[EXTREME HARD ]These diamond drill bits are made of industrial grade carbon steel with nickel-plated coated body to resist corrosion. A thicken diamond coating on the tops offers superior cutting strength for maximum drilling outcomes. [EXTRAORDINARY SHARP]Each diamond has a and exact finish that lower the incision resistance and drill pressure, increases the , and effectiveness of water lubrication. for making clean and precise holes on glass or ceramic and considerably extending drill bit life. [ CLEARANCE HOLE]These glass set along the drill bit facilitate the entrance of cooling water and escape of chips and other particles from drilling. Makes the drilling process easier. [WIDE USAGE] 5 size drill bits (4mm/0.16inch , 6mm/0.24inch , 8mm/0.31inch , 10mm/0.39inch , 12mm/0.47inch ) included with this glass drill bit set to meet demands. Perfect for drilling glass, tile, porcelain tile, ceramic tile, brick, and stone. length: about 2inch colour: silver Material: carbon steel size: 10x6x3cm Package Contents: 5*Diamond Coated Drill Bit Attention: keep the speed within 800-1000 per , low drill pressure and increased use of water lubrication will extend drill bit life. And keep adding water when the diamond drill bits are working on the glass or . Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.