I needed to fit a handrail in my shower through existing porcelain stoneware tiles. One of these hollow drill bits made four holes easily and made nice smooth holes. They are more like a hole saw than a drill press. While drilling, I sprayed water on the drill bit every few seconds. I had a piece of 1/16" thick scrap aluminum with a 1/4" hole that I clamped onto the surface of the tile to use as a guide to prevent the bit from sliding across the surface of the tile . It only took a few seconds to cut the surface deep enough to hold the bit in place, then I removed the guide. I was pleasantly surprised at how much easier it turned out to be than I thought. It was much cheaper than other diamond core bits.