I used these drill bits to drill 4 inch deep holes in a limestone slab along with wedges and spring spacers to separate many sections of it. These bits have no problem with limestone. I drilled at least 100 holes with this set of 5 and put them in a bucket of water after each hole. They're all holding up pretty well and I don't expect them to suddenly stop working. A very good buy for me and I highly recommend Kalkstein. I will add that they got tired pretty quickly. I'm not a patient person. I would happily buy the same bits in slightly longer lengths if I could pay the same price per inch. Very satisfied! Thanks very much!