The loosening of threaded connections, joining two moving components in machines is a well-known phenomenon. The problem is more common in the machines which undergo intermittent motion, i.e. switchgears, printing machinery, etc. A theoretical model is proposed to study the loosening caused by the impact loads and investigate the effect of different parameters which intensify its cause. It is concluded that the duration of the applied load, the lead angle and surface friction have an important role in loosening processes.