Did you have it threaded at the full diameter of the axle? Usually when I make an axle I turn the threaded part one size smaller than the main axle. That way the threads aren't a close fit to the bearings and you don't screw them up. If it's fine-thread then the threads weren't very deep. You could probably machine the old threads off and thread it one size smaller and get new nuts.

Don't know what size threads you have, but if you can find a "thread file" in the right size you can probably fix them up pretty easily:

http://www.amazon.com/General-Tools-Thread-repair-75--30/dp/B0017R1DOM/ref=sr_1_6?s=automotive&ie=UTF8&qid=1396457647&sr=1-6&keywords=metric+thread+file