How tight should a fastener be? What torque setting is appropriate?
This is not a simple question and many factors will affect the torque that should be used. Tightening a fastener to a given torque will usually result in some small amount of stretch to the fastener itself; if this stretch exceeds the tensile strength of the fastener either during the tightening process or subsequently with operational load added, the fastener will fail. The torque is therefore important and many engineering applications will specify the correct torque settings. If these are not respected, failures can result which could easily have safety implications. If you are servicing or building a piece of equipment, especially if it has any safety-related aspect, you should always try to obtain the tightening torque values that were specified by the designer and to follow them carefully. Considering the general principles, the type, size, thread and grade of the fastener itself naturally all have a significant effect on acceptable torque values (mild steel fasteners could fail
