In the previous two articles on the subject of fastener tightening, we looked at two methods of pre-loading threaded fasteners - torque control and the turn-of-nut method. The method of torque tensioning remains a favourite; anyone with a torque wrench can use this method, but a lot of engineers are wary of it because of the variability of factors that influence the load. Friction is the main variable; it changes with materials, surface finish, lubricant, and is often worryingly...