On the Coefficient of Friction and Adequate Tightening Force for Screw Threads

Abstract

In order to give adequate tightening force for a bolt joint, sometimes a torque wrench is used. The objects of the present paper are to find the true value of coefficient of friction between bolt and nut and to estimate the adequate pre-fastening force which is necessary to decide what torque indication should be given to the torque wrench. As the result, the author recommends the ordinary value"0.1∼0.2"for the coefficient of friction and one-half the yielding stress of the material calculated by the core section of the bolt for the pre-tightening force.