I found that the key to using my granite slab was to use it on a drill press at high speed and have a second person spray water with a nozzle to cool it down. At first I went relatively slow at the speed of the drill and wasn't happy, then I switched to high speed and the bit went right through the plate. You probably wouldn't buy a few if you were a pro, but for personal use every few years it's great! I used it for a single hole faucet.