Nut

A nut to be fastened onto a bolt, characterized in that

• the nut comprises:
• a nut main body having a substantially cylindrical shape and constituted by a plurality of nut segments obtained through segmentation of the nut main body in a circumferential direction around an axis of the nut main body wherein the bolt is expected to be inserted along the axis;
• an outer cover comprises a polygon base and a stopper that are configured to respectively cover an outer circumference and one end face of the nut main body;
• a restraining ring configured to abut against the other end face of the nut main body for restricting movement of the nut main body in an axial direction in the outer cover while allowing the nut main body to only expand and contract in a radial direction in the outer cover;
• an inner cover comprising a restraining plate at one end portion of the inner cover, the restraining plate being configured to restrict a position of the restraining ring, the inner cover being accommodated in the outer cover and configured to cover the outer circumference of the nut main body;
• and
• a ring-shaped spring disposed on an inner wall of the nut main body and configured to bias the nut main body to cause the nut main body to expand radially toward an inner wall of the inner cover, wherein
• a protrusion protruding in a circumferential direction is formed on the inner surface of the inner cover,
• a groove is formed in a circumferential direction on an outer surface of the nut main body in a manner in which the groove is capable of engaging with the protrusion and accommodating the protrusion, and
• the protrusion has a slant surface and the groove has a slant surface, the slant surfaces being configured to contact each other on the same side in the axial direction, wherein
• the stopper of the outer cover has a through-hole of which an inner diameter is equal to or greater than an outer diameter of the bolt such that the bolt penetrates the stopper in the axial direction of the outer cover,
• the polygon base has an outer shape that is polygon such that the polygon base fits in a tool such that the outer cover makes a rotation in either a clockwise or anticlockwise direction by the tool,
• the nut main body is arranged to be in one of three states of arrangement and is interchangeable to each of the other states as defined below:
• an insertion state constituted by a state in which the nut main body is expanded radially by the ring-shaped spring and the protrusion and the groove are in engagement with each other,
• an intermediate state constituted by a state in which the protrusion and the groove contact each other only through the slant surfaces and the nut main body contracts radially against the ring-shaped spring, and
• a fastened state constituted by a state in which a leading end of the protrusion is in abutment against an outer wall surface of the nut main body except for the groove and the nut and the bolt are fastened together, and
• a transition between the insertion state, the intermediate state, and the fastened state is made by moving the inner cover in the axial direction.