Swiss-made medium-fine grit twist drills are the ultimate for drilling stones, pearls, glass, or ceramics. Use with standard handpieces and a small amount of water as lubricant. Diamond drill bits with 3/32 Inch diameter shanks Diamond coated twist drills will drill through stone, ceramic, glass and other hard non-metallic materials, as well as fiberglass, hard plastic, graphite and carbon. They are not generally a good choice for granite. Diamond coated drill bits are coated with one layer of fine diamond particles. Because of the nature of the diamond coating process and the random positions the diamonds sit in, the drill diameters may vary.