Bought for drilling porcelain tiles. This tile is very hard. My tiler also installed shower doors. It took him half a day to drill 10 holes. for wall frames and went through 2 diamond bits ($26 each). I wanted them to install the railings themselves (they say for tiles). However, these bits went everywhere and were useless. I ended up having a 1/4" diamond drill bit from Home Depot for the 6 holes I needed. (Milwaukee, 3 p.m.) Slow. About 10-15 minutes per hole, but it worked. The drill bit was also worn and the last hole took longer .Note: don't worry, maybe they work on ceramics and glass, take a diamond crown and you need to start at a 45 degree angle to start the hole (notch) and it gradually Move to 90 degrees Dive further into the water to keep the beat cool.