I think I've posted about these before in response to the how do I get screw out question. While I only end up using mine maybe a few times per year, they've been like magic compared to other methods. I never seem to be able to get those screw extractor things to work. Cutting slots in broken shafts seems to work sometimes, but I've found this thing to get a better overall grip on more of whatever is exposed to allow for more force to be applied.