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Originally Posted by sperry
I thought the fastener requires a certain amount of torque because lower torque would allow the threads to back out.
For example, a high-grade nut/bolt would require more torque than a lower grade because otherwise the threads would not stretch enough and therefore there wouldn't be enough friction to keep the nut on.
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I only think a change in thread pitch would require change in torque. The torque is generated by the friciton between mating surcafaces regardless of the stretch of the materials, so the same amount of friction would keep something with the same thread just as tight.
Now if the higher grade fastener had a higher expansion rate under operating temperatures, then it might need more torque.