US Patent 7371027 Fastening tool and fastening bolt

In a fastening tool in which fastening members may be inclined as they are threadedly inserted together whereby almost no displacement load is applied to the members, a member having a bolt through hole with a tapered seat surface, and a fastening bolt that includes a bolt body provided about its outer periphery with a male thread, and a head provided on an end of the bolt body that has a diameter greater than that of the bolt body, in which the head has a lower outwardly curved tapered surface whose diameter is reduced toward the bolt body so that the lower surface abuts against the tapered seat surface when the fastening tool is used.