4 pc DIAMOND DRILL BIT SET for GLASS ROCK STONE TILE SMALL SIZE 1/8" - 1/4" Drill glass, marble, masonry, rocks, concrete etc... Super duty diamond coating on nickel plated high speed steel will give you excellent results even in semi-precious stones. Sizes: 1/8", 5/32", 3/16", and 1/4" Note: use on a low speed with coolant (water/oil)