80% - 85% of clamp load and torque is affected by the surface friction on the threads and under side of the head of the bolt/nut...
Every time a bolt or stud is torqued, it receives some degree of permanent stretch... Eventually that stretch adds up and will compromise the integrity of the bolt/stud...
On connecting rod bolts fastener engineering allowed only 5 torque cycles and then recommended that they be scrapped after that... we left two torque cycles for outside the plant, one for service, and one for rebuild - however that didn't account for plastic gauge...
So we were only allowed to torque a rod and cap twice on the assembly line because they already had one torque/clamp cycle when the rod and cap were machined on the rod machining line... So we could only re-use a connecting rod once before having to scrap it at the engine factory...
