In mechanical structures, a lot of bolts and nuts have been used. Sometimes loosening accidents happen in the structures under several types of loadings. Recently, the cause of the screw thread loosening is being elucidated. However, the effect of some parts for preventing the loosening in bolted joints such as spring washer, double nut and so on is not fully elucidated. In this study, the experiments were carried out to measure the reduction of axial bolt force in the bolted joint with some parts for preventing the loosening such as the spring washer, the toothed washer, the double nuts, the eccentric nut, and so on under the transverse repeated loadings. The test machine used was Junker’s type loosening machine. Then, the effects of the washers and some types of nuts are evaluated on the loosening of bolted joints. It is shown that the performance for loosening is getting better as the initial clamping force increases and the effect of the washers is not found on the loosening. However, the effect of eccentric nut is substantial on the loosening. In addition, the loosening tests according to NAS were also carried out. No effect of all the washers mentioned above is found due to NAS testing. Discussion is made on the effect of the parts for preventing the loosening mentioned above.

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