Bought to finish a very complex bathroom, drilled more than 10 holes on each of the two drill bits with no problems. Considering how much they cost in store they were perfect for me. I used 1/2" thick porcelain stoneware, I had to drill a bigger hole and use a carbide bit, literally 45 minutes to drill. These diamond crowns are drilled in a few minutes. For those inexperienced with these bits, keep them wet and work slowly. I drilled a 2x4 bracket with the right size hole to attach it to the tile as a guide.