The method is based on the use of the acoustoelasticity phenomenon, the essence of which is the dependence of elastic moduli on mechanical stresses. The speed of elastic waves is used as an information parameter. By changing the propagation velocity of the corresponding elastic wave mode, it is possible to estimate the stresses arising in the threaded joint, and hence the degree of tightening. Tightening the threaded connection can cause the stud or bolt to elongate, which additionally contributes to the measured parameters. All of these factors influence the measurement results.
The set of equipment consists of a primary converter, a generation-receiving unit, a control computer and software. It is possible not only to monitor the tightening process, but also to diagnose the condition of the tightened studs.

The advantage of the proposed method lies in the use of several modes of elastic vibrations. The change in the propagation velocity difference due to tightening is measured and converted to voltage units.
The cost of a set of equipment does not exceed USD 10,000.