Each diamond drill bit has built-in wax lubricant, which can melt and cool the drill tip, prevent diamond loss, and extend drill bit life. You can make the drill bit to cool after each hole to maintain optimal performance. The package includes 2pcs 3/16inch (5mm) drill bits, 2pcs 1/4inch (6mm) drill bits, 2pcs 5/16inch (8mm) drill bits, 2pcs 3/8inch (10mm) drill bits, and 2pcs 1/2inch (12mm) drill bits. The 10pcs combinations and quantity for your long-term use and replacement. The built-in round is compatible with the most popular electric drills, angle grinders, and bench drills. The side groove design removes debris faster, and the depth marks on the side are practical for precise operations. The dry diamond core drill bit adopts vacuum brazed diamond technology to drill clean holes in types of tiles, ceramics, , porcelain, glass, marble, stone, masonry (not suitable for wood). Product Name:Diamond Drill Bits Set Colour:Black Material:Diamond Size:3/16inch (5mm),1/4inch (6mm),5/16inch (8mm),3/8inch (10mm) and 1/2inch (12mm) Package Contents: 1set * long drill bits for wood Only the above package content, other products are not included. Note: Light reflection 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.