PURPOSE: Not to materially damage a bolt head part and a bearing surface as shearing stress and tensile stress separately correspond by fixing the bolt head part and the bearing surface by separate screws or welding.

CONSTITUTION: Duralumin 8 is sandwiched as a cushioning material in a cavity part of a head part l, a head end 4 of a shaft part 2 is inserted in the cavity part, and the head part 1 and the shaft part 2 are connected to each other. As length of the part 4 of the inserted shaft is extremely short in comparison with the whole length, damage by shearing stress is geometrically hardly caused. Additionally, as the head part 1 and the bearing surface 7 are fixed by separate screws 5 or welding, it is possible to avoid concentration of stress on a material and an under-head part in conventional forge machining and damage is extremely hardly caused.