New analytical formulation for torque specification of bolted joints considering external taper thread and internal parallel metric thread

Specifying and applying the correct tightening torque to achieve the required tightening force is essential for obtaining a reliable tensile bolted joint. In order to avoid failure of any component and/or self-loosening, the effective length of engagement between the threads plays a major role. The analytical procedures available for these applications concern the assembly of internal and external parallel threads. However, there is not analytical procedure for an external taper thread with an internal metric parallel thread. So, the present work develops an analytical procedure for calculating the length of engagement, the number of threads effective engaged, the percentage of the maximum assembly preload supported by the first screw thread and thus the tightening torque to be applied during assembly of an external taper thread with an internal metric parallel thread. Results showed that, in this case, just a few threads effectively engage and the 1th engaged thread supports the major part of the clamp load (approximately 35%). To clarify this procedure, there is a solved example at the end of the article.