In order to cut M10's tap into a small iron block, it is necessary to pierce with a small desktop drilling machine, but since the drill of φ 8.5 is too long to process, it was searching for a short drill. Because this nodril is for electric drills, not only the shank diameter is small but also the length is short, it is easy to use even on a tabletop drilling machine.
Just opening a couple of them made the sharpness fall. It is expensive to be disposable. I'm planning to polish it again, but can not you make it to last longer?