Attachment device

An attachment device for rotatably attaching a member (B) to an object (A), comprising:

• the member (B);
• the object (A);
• a bolt (2);
• and
• first and second nuts (3, 4) having female thread holes (3a, 4b) into which the bolt (2) is screwable,
• wherein the bolt (2) is fastened to the object (A) by using one of the first and second nuts (3, 4);
• the other nut is adapted to threadably mount on the bolt (2) after the bolt (2) is fastened to the object (A) by using the one nut;
• the first nut (3) includes a first support surface (31a) capable of supporting a first side of the member (B) and a boss (32) axially protruding from the first support surface (31a) toward the second nut (4) for rotatably holding the member (B);
• the second nut (4) includes a second support surface (4a) capable of supporting a second side of the member (B) opposite to the first side, and an engagement recess (41) provided in the second support surface (4a) into which the boss (32) is fittable;
• an outer peripheral surface of the boss (32) is eccentric relative to the female thread hole (3a) of the first nut (3) or an inner peripheral surface of the engagement recess is eccentric relative to the female thread hole of the second nut such that, when the boss (32) is fitted into the engagement recess (41), a circumferential portion of the outer peripheral surface of the boss (32) engages a circumferential portion of an inner peripheral surface of the engagement recess (41) such that, in each of the first and second nuts (3, 4), a pressing force in a direction perpendicular to an axis thereof is produced;
• and
• each of the outer peripheral surface of the boss (32) and the inner peripheral surface of the engagement recess (41) in engagement with each other is formed into a straight cylinder shape such that a constant tightening torque is produced in the first nut (3) by the pressing force even when a fit depth of the boss (32) with respect to the engagement recess (41) changes in a predetermined range.