drilled hard porcelain stoneware. I don't know the Pei rating but I think it was a 2 or 3. Starting the hole was a little risky but with the advice of another review I drilled a hole large enough for a drill length of the block of wood and held it to start the hole where I wanted. Walking got better. I can't comment on their lifespan due to the price and used a new drill bit for each hole to minimize risk, but I think it could have been done with more than one. He kept spouting water, often stopping so as not to break the tile. As others have not noticed, it was probably about 20 minutes per hole. It was worth not cracking new tile in the shower, and a pack of more bits costs less than one at Home Depot. I would recommend them.
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