A hypothesis was presented concerning the effect of the axial residual stress at the first thread root of a bolt on its fatigue strength. However, this has not yet been verified since the residual stress which may exist locally around the thread root cannot be measured or estimated with sufficient accuracy. This study aims to clarify the relationship between the residual stress and the fatigue strength quantitatively. In this report, the residual stress which can be estimated by FE analysis is induced by preloading on the thread root of lead-less (axisymmetrical) bolt quenched and tempered after thread-rolled. The results from fatigue tests in low mean stress condition (Rs = 0.1) show that the preloaded specimens have higher fatigue strength than non-preloaded specimens. However, the effect of residual stress is much smaller than estimated by the hypothesis, and this might be caused by the stress concentration, which cannot be taken into account by axisymmetrical FE analysis due to the construction of threaded adapter.
