For tightening torques we mean those reference values according to which each nut, bolt, stud, etc. it should be tightened so as to achieve the ideal fixation for that type of element.
The values to follow refer to the table of preloads and base pairs for generic fasteners. Each resistance class has its own specific tightening torque.
The international reference tables available online link the diameter of the thread with the tightening torque expressed in newton / meters.
The Torque Wrench is the most widespread tool for tightening any fastening element to the right torque values and "warns" it when the set torque value is reached.