In order to achieve quality products, certification of production processes is currently required in companies. It is possible to mention the procedure of screw tightening. To obtain a certificate, it is necessary to check in the company the technological assembly procedure and the equipment of the workplace with jigs and tools. It is necessary to check whether all provisions of regulations and standards are observed during the assembly of the product. In the case of screw connections, it is necessary to carry out experiments to verify the correctness of the tightening torque and to determine the Torque-angle curve. It is often required to assess the quality of threaded surfaces after disassembly of the product on a metallographic cut. This paper describes the certification procedure of tightening the main screw connection of a selected product. Without the granting of the certificate, it would not be possible to proceed with further assembly.