Self-loosening phenomena in bolted joints result in serious accidents. Thus, several types of parts for preventing self-loosening have been applied to important bolted joints in mechanical structures. Recently, the prevailing torque type nuts, in which the friction coefficients are increased at the screw thread and the bearing surfaces of nuts, have been paid a lot of attention and widely used in bolted joints for preventing self-loosening. In this paper, coefficient of friction between threads and bearing surface, and the self-loosening characteristics of bolted joints with the prevailing torque type all-metal hexagon nuts under axial repeated tensile loads were measured.
