I accidently put a nut on a stud that was the wrong thread size (coarse to fine) and screwed up the first few threads and now the orignal nut will not screw on. Is there anything can do to get the threads back? I can't take out the stud. Thanks

 

In the future, don't do that. Force the correct nut on if you have to. Then replace the nut with a fresh one. Or buy a die in the right thread.

 

Get a tap and die (SP?) set and re-thread the bolt.

 

Why can't you replace the stud?

Something that I did once on a threaded rod that couldn't easily be replaced, but had messed up threads at the end... I didn't have a tap for it, so I took a correct nut, and split it in half (hack saw, grinder, what you have handy), then put he two halves on the good threads, and used a clamp the turn it off... thus cleaning up the threads... Worked too!

 

Damn....that sounds like a good idea. I will have to try and remember that.