14mm concrete drill bits for making holes for splitting various soft to hard stones for disposal with 9/16" feather/wedge tools. I didn't try them on concrete. The fit between the holes and the feather/wedge tools needs to be precise or the tools can't gain purchase on the stone. The bits from UK Drills were 1/2 the price of DeWalt Extreme 2s and were fine on sandstone. Sadly, the tip "wings" that provide the 14mm hole diameter wore away on any harder stone so the splitting tools couldn't be inserted far enough. Verdict: not all masonry drill bits are created equal.