I make a lot of stone and marble as a hobby. I bought them to cut different sized circles from different types of stone and marble. The "diamonds" encrusted on these bits are too thick and eat away at a lot of material, creating too much waste. It is also difficult to start a hole even when installed in a drill press. Attempting to start a cut at an angle (as recommended by the manufacturer) is extremely difficult as the drill will slide across the workpiece and damage the surface with unwanted cuts/cuts. I've always water cooled the chisel and workpiece to remove stone dust from the work area, but that doesn't even seem to help.