I used these diamond core bits to drill 4 holes in porcelain stoneware about 1/4 inch thick. The bits worked with my dremel but I had to use 1-2 bits for each hole so make sure you have enough on hand to complete the job. One of the bits bends when drilling, so these bits are not top quality, but they get the job done for a low price. I couldn't find better bits in this size so I ordered them. This drill appears to be slightly smaller than the advertised 5/32", so I had to increase the diameter slightly to fit my concrete screws. Be sure to start drilling at an angle and then straighten so the drill does not slipped. emerge.