Hey thanks Finky198 and T45.
Just a follow up question:
Which rethreading die would be able to "stand up" mashed threads?
First caveat, is nothing works on hardened bolts like grade 8 or 12.9.
second, a reforming dies needs the bolt to be close to spec in general to work. much like a tap-drill needs to be close to correct spec. the tools only move so much metal.
third, the colley type and adjustable cutting type may be of use if the damage is beyond the re-threading die. they are better than non-adjustable as the do less damage on the threads during approach to the damage site.
in general, the better-quality rethreading dies are quite good. they are made out of proper hardened toolsteel and are much better at making a crisp rethread.
The kastar type are more prone to clear out the groove of the thread pretty well without forming as strong on the peaks. This is why the function pretty good as cleaners. And also very minor damage they can straigten out.
The cutting dies will cut dmaged threads out of the way, which sometimes is needed to salvage a bolt--ie, because maybe the damage is on a longer bolt and you can still get away with some good threads elsewhwere. The collet type may allow you some flexibility on approach (as noted above).
The round/split dies allow you to not trash good threads on the approach and offer some flexibility to not remove the maximal amount of metal unless its actually needed.
so having choices is helpful, but not always possible. Cross-threading fasteners is a quick way to run up a big expense and sometimes the prevention is worth it.
