Nearly stripping a UNC thread in my Muncie gearbox alloy case started me thinking - mainly because the threaded hole isn't blind, it goes right through the case . So cleaning up the thread or an insert would require stripping down the whole box which is way beyond my skills.
So I just scraped out any chips VERY carefully with a fine pick and shortened the bolt to only go into the undamaged part of the thread.- then I lockwired them to be safe!
The shortened bolt only has a few turns of thread but I recall seeing somewhere a formula which aid something like " you only need 1 1/2 times the bolt diameter of thread to get maximum grip."
I think it is saying that since the thread length is pi D times the diameter and all the stress is in the top part of the engagement .
Has anybody else heard of that rule?