I bought 10 of these expecting to burn through a few while trying to drill through porcelain tile to fit a cabinet flange. straight at an angle to cut a groove in the tile, and when it is passed through the top surface, loosen the drill in a vertical position to drill directly into the tile. No high speed required, just slow and steady with some water. If you see smoke/steam, you are about to fast. After about 10 minutes I had drilled the four required holes perfectly. I could have used one nozzle for all four, but the stem had a stuck porcelain "core sample" after the first three, so I used the second nozzle for nothing. Rescuer. Considering the cost of one bit at the local department store is almost three times that of all ten, they're worth the money.