This self-locking series corresponds in all points to the conventional series, the screw threads being locked by polygonal deformation of one or more turns of the thread. This deformation results in a powerful locking on the sides of the screw thread and counteracts the unscrewing effects of dynamic stresses, vibrations and thermal loads. The locking torques obtained are comparable with the values indicated in standard ISO 2320. The stainless steel self-locking thread insert is recognised by its red colour.