In the previous papers the author reported the strength of bolt-connection under repeated load in the case the external load acted only along the axis of bolt. But in the case of practical bolt-connections, it may be well said that all of the external loads acting on bolt-connections may contain the bending stresses besides the tensile stresses, and that the stiffness factor ratios of practical bolt-connections may have very small values as 2 or 3. The author did not treat the bolt-connections having such smaller stiffness factor ratios as related above. In this paper he has obtained the stiffness factor ratios on the connecting rod used in the motor car, as a practical example, and established a new empirical formula of stiffness factor ratio suitable for such a practical connecting rod as this.