I was pleasantly surprised at their longevity! They look delicate as they look thin in the diamond shell, and not chipped , as could crowns on concrete. However, I cut 4 holes with the same bit through thick stoneware and 1/2" backing with no problems and no sign of wear on the bit. Made a template out of a 1x6 piece using the pre-drilled with a wood drill bit, attached it to the bathdeck, used a standard household spray gun to keep the hole wet and the drill bit cool as he drilled each hole, applying even but light to moderate pressure on the drill bit, crisscrossing right through each hole Don't be greedy for downward pressure and don't skimp on the water Again, no noticeable bit wear after 4 holes I haven't noticed any slippage, full run dshafts could be improved with chamfers, but no problem this time.