All good info. One more thing I didn't see in any of the threads. The smooth appearing metal in a joint build-up may look smooth to the naked eye. But look at it through a high powered microscope, and it looks like the view crossing the Rockies. It's the tops of all those peaks that get worn down or permanently compressed during operation, and that relaxes the stretch of the bolt thus loosening the joint.
And remember, torque is just an approximation of bolt stretch. Take 100 "identical joints", strain gage 100 bolts (only done in a lab), torque them all to identical values, and you will have 100 different measures of bolt stretch (strain). We did this often in the auto lab where I once worked.
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Rich Bond
Just a wishful observer
Gave up awaiting AOPA/EAA exemption request
2015 =VAF= Contributor
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