[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 hole saw has a smooth and exact finish that lower the incision resistance and drill pressure, increases the sharpness, and effectiveness of water lubrication. Excellent for making clean and precise holes on glass or ceramic and considerably extending drill bit life. [LARGE CLEARANCE HOLE]These glass hole saw 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 varied 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 various demands. Perfect for drilling glass, tile, porcelain tile, ceramic tile, brick, and stone. Total length: about 2inch colour: silver Material: carbon steel size: 10x6x3cm Package Contents: 5*Diamond Coated Drill Bit Attention: Please keep the speed within 800-1000 per minute, low drill pressure and increased use of water lubrication will extend drill bit life. And please keep adding water when the diamond drill bits are working on the glass or ceramics.