Have you ever stripped the head of a bolt or perhaps even break it right off? I’m willing to bet that if you have, you have most likely had to deal with using an extractor to try and get it the damn thing out. This usually involves drilling a hole in the bolt and trying to use this odd spiral cone with a bolt head on it to twist the bolt out. While this is basically all you can do let me make one suggestion that may get that bolt out. When you try to drill the hole why not try using a reverse drill bit? Most of the time this will extract the bolt without having to use the cone shaped extractor. Worst case you made a hole in the bolt that you need anyway. In my experience this works more often than not. So next time you bark your knuckles as a result of a broken or slip on a stripped bolt try using a reverse drill bit, it certainly won’t make things worse.