Torque

Torque is the rotational force applied to a fastener when tightening or loosening it, typically measured in inch-pounds (in-lb), foot-pounds (ft-lb), or newton-meters (N·m). In fastening, torque is commonly used as a practical way to control how tight a bolt or screw is during installation. As torque is applied, it helps stretch the fastener slightly and creates clamp load, which is the squeezing force that holds the joint together.

Torque matters because too little torque can lead to a loose joint, vibration loosening, leaks, or fatigue failures, while too much torque can strip threads, crush materials, or cause the fastener to yield or break. The torque needed depends on factors like fastener diameter and grade, thread pitch, lubrication, coatings, and the material being clamped. Because friction in the threads and under the head consumes much of the applied torque, lubricated and dry fasteners can reach very different clamp loads at the same torque value, so torque specifications should match the intended finish and installation conditions.