My experience: an M6 broken off when tightening. First of all, a very good quality metal drill bit. I drilled with one for 10 zl, but when I bought one for 20 zl, it only made sense. I used a diameter of 3.0, but it is minimally too much. I think 2.5 would have been ok. The second thing is that you need to drill as centrally as possible, so that the screwdriver has something to grab onto. Third, you need to drill a minimum of about 0.5 cm so that the twist-off has something to grab onto. Fourth, the twist-off with a slanted thread, as in the photo, rather than with a straight thread, which clasped worse and quickly began to spin. Both bought at the market for $20. With these parameters, I used the second largest screwdriver, because the smallest one, however, was too small. You have to take it easy, a lot of space and a lot of time.