The proper pre-loading of cyclically stressed fasteners is crucial to their performance. By pre-load, I mean the tension applied to a fastener through tightening before any service loads are applied. If we are to optimise the design of the fastener for minimum mass, this is an especially important point. If the load is too great, we will overload the fastener or the joint; if it is too little, we may fail the joint through separation. Of course, in optimising the design of any given...