Rounded off derailleur hanger mount bolt
 

This particular bike was converted to single speed, so the hanger isn't used for anything, but while I was doing other things to the bike, I thought I'd just make sure that bolt was snug. Without much torque at all, the 5mm allen key slipped in the bolt. It may have already been partially rounded before I touched it, but in any case, I wasn't able to remove the bolt to replace it. It only rounded more in trying to remove it.

How would a shop deal with this? I could use a dremel wheel to cut a slot in the bolt, but it would most likely cut into the hanger as well. Should I just leave it as-is and forget about it?

Never Fix A Running Piece! You could try pounding a Torx® key or fractional key into the recess, or epoxying a sacrificial 5mm key into the bolt to use for removal.

If you ever do have to remove it try using the appropriate size torx wrench/socket. Usually work great on stripped allen socket heads. .

Is the stuck bolt alone, without a der around it? It is Steel? A photo would add more details. Andy

Thanks for the suggestions. Yeah, it's by itself and easily accessible once I remove the rear wheel. I could probably drill straight through it if necessary.

Yeah, doesn't seem like my best move in retrospect.

Does the bolt head raise above the drop out face? Could the head be grabbed with a lock jar pliers or pipe wrench? Andy

No, it's completely flush with the face. I'm still waiting on the new bolt to arrive before I try anything, but I decided to order a small set of screw extractors called the Alden 8440P Grabit Pro. Figured I'd give those a shot first, and if that fails, maybe try the epoxy idea someone mentioned earlier...maybe with JB Weld.

Screw extractors usually give very disappointing results. If you do use that, remember get as much downward pressure as possible. Consider a cheap impact driver as well, something you hit with a hammer to turn the bolt

https://www.amazon.com/TEKTON-2910-2...24752796&psc=1

I like the hammer and a Torx bit in there idea the best.

On cars I've welded a new nut onto the top of rounded or even broken bolts. Would be near impossible to do in your case.

Well, the extractor set worked out. I tried at first with a manual driver and downward pressure, but I couldn't turn it. I then put the extractor bit in my electric impact driver and after a few seconds, the bolt came loose. Put the new bolt in and all is well.

Love a happy ending.

Thanks! I'm glad I didn't have to resort to anything more extreme. When I was shopping for extractor bits, I read a lot of horror stories...bits breaking and whatnot. I'm guessing they don't work well when the bolt in question is crossthreaded or old and corroded, maybe tightened 20 years ago and then rusted over. Thankfully mine was just a relatively recent and cheap bolt whose head stripped out a little too easily.

The most important thing I needed to learn with extractor bits was one must drill out as much of the stuck bolt as possible. Once you break an extractor bit in a bolt any future drilling is over.

The article recommends left hand drill bits.

Catalog

For your case the extractor bit and impact drill was the near perfect solution.