This diamond-impregnated core-style bit features great long life and is ideal for drilling in both flat and contoured surfaces. Diamond grit a full 360 deg around the circumference of the bit allows it to be used in a rasping action to enlarge a hole if needed. Holes on the side of the bit allow the removal of glass dust from inside the bit. Each bit is packaged with Dremel® cutting oil to increase the speed of cut and prevent damage to the bit from overheating.