If you go by the book u-bolts should never be reused, once you pull them off simply discard them.
Please don't rethread your old ones.
You can have new u-bolts made at a big truck parts place and or a spring shop. They are not expensive, and all the ones I've had made even come with new nuts and hardened washers.
Could also have them made at
http://www.eatonsprings.com/ I've used some from them as well.
Grigg
