Tightening torque can vary depending on certain parameters, one of the most common being the elasticity of the materials being used in the application. The resulting torque is referred to as Residual Torque.  In certain applications, a specific torque is required, and this must not vary. In these cases, it is necessary to check the residual torque periodically and if required to tighten the clamp again to bring it back up to the required tightening torque.