These are like a regular twist drill but coated in diamond grit making them possible to use on hard materials such as stone, glass, ceramics, porcelain, and shell. They are designed for enlarging holes rather than drilling holes.   Perfect for enlarging holes in pearls. They have diamond grit running along the tip and sides allowing them to remove material horizontally as well as vertically and are especially good for widening existing holes. Used by Jewelry Designers for drilling clean holes on Beach Sea Glass, Sea Shells, Rocks, Marbles, Stones, etc.Practical – Suitable to be used with hand drills, flex shafts and dremels.Experience needed, you may break few bits during practice. Use with water – do not run dry.