Three Methods of Verifying Torque Specifications

Once a torque specification is determined, the joint should be audited to verify the product has been fastened to the specified torque. There are three common torque test methods that have been established to provide an accurate reference to the applied torque.

1) First Movement Test – Once the fastener has been tightened, employ the use of torque measuring tool. Mark the tightened fastener and surrounding application. In the tightening direction, begin to slowly apply force to the tool until the first movement in the fastener is noted. The reading recorded is a good indication of the original torque applied to the joint. This is the best way to determine residual torque.

2) Loosening Test – This is a similar process to the first movement test described above, except instead of the tightening the fastener, the torque is applied in the direction that loosens the fastener. At the point the fastener breaks loose, the torque reading is recorded. The torque value to loosen the fastener is the approximate torque that was applied to the joint.

3) Marking Test – Once the fastener tightened, mark clearly the surface of the fastener, nut or bolt and continuing the mark onto the surface being clamped for reference. This time loosen the fastener and retighten until the marks on both application and fastener are aligned. The torque required to return the fastener to its original location is the reference to the original torque applied to the fastener.

Which torque testing method do think is the best to use and why?