To provide a bolt and a nut with enhanced security.
In a head portion 1, torque receiving parts 2 receiving rotating torque from a dedicated tool and torque reception inhibition parts 3 each having a curved outer face and inhibiting the torque receiving parts 2 from receiving rotating torque from a tool other than the dedicated tool, are alternately disposed around an axial center of the head portion 1. One of both side faces of the torque receiving part 2 serves as a tightening torque receiving face 21 for receiving tightening torque from the dedicated tool, the other face serves as a loosening torque receiving face 22 for receiving loosening torque from the dedicated tool. An outer face other than the both side faces is a curved face. The loosening torque receiving faces 22 are disposed at an angle inhibiting reception of loosening torque from a holding tool even when the head portion 1 is held across the axial center by the holding tool.
ARAKI HIROTO
ARAYA MASAHIRO
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