How to improve both anti-loosening performance and fatigue strength of bolt nut connections economically

•Several F-T relations of pitch difference α nuts are obtained by EXP and FEA.•Anti-loosening performance of pitch difference nut is controlled by α and n.•Larger thread number n and smaller α is better for fatigue and anti-loosening. In this paper, how to improve both anti-loosening and fatigue strength with low cost is newly proposed for bolt-nut connection. The authors’ previous study clarified that the most suitable pitch difference α=α1 for the fatigue strength is smaller than the most suitable pitch difference α=α2 for the anti-loosening. In this paper, toward improving both fatigue strength and anti-loosening, a larger nut height coupled with pitch difference is studied through experiment and FEM analysis. It is found that with increasing the nut height, the suitable pitch difference for the anti-loosening α=α3 decreases without changing the suitable pitch difference for the fatigue strength. Therefore, a larger nut height with the pitch difference α=α3≈α1