I recently went through this nightmare myself. The stud on the DP broke, and I had to use a tungsten masonry bit to drill through the old stud. Cobalt and extremely expensive carbide drill bits wouldn't get through it, but the 6 dollar tungsten masonry bit cut through it like butter (it was the spoon shaped bit). The metal was so insanely hard that I couldn't tap it, so I just used a bolt/washer/nut and called it a day.
