A lot of times when working on a project it’s easier to just replace a bolt or stud rather than restore it. However, sometimes you come across a hard-to-find bolt or you just don’t have time to run out and find a replacement so restoring threads is easier.
Whether your bolt is cross-threaded or has threads that are flat, there’s a fix. The first tool you could use is a thread file, or thread restoring file. This tool actually has 8 different sizes of thread pitch on it, everything from 11 up to 24. Taking the flat threads and running it over the file will get rid of them.
If you have a cross-threaded bolt a die from a tap and die set installed in a t-handle will do the trick. Simply tighten the die in the tool and run your bolt through it.