Patent ID: 8747039

Claim:
An apparatus comprising: a nut; a bolt comprising a foldable part provided at a tip of the bolt, the foldable part being foldable from a direction along a bolt axis to either side around an axis perpendicular to the bolt axis; a knob that applies a torque and comprises an odd number of grooves formed at a tip surface of the knob, each of the grooves being configured to receive the foldable part and arranged radially with equal angular intervals with a center at a screw hole of the nut; and a clutch provided between the knob and the nut, wherein the clutch mechanism rotates the knob freely with respect to the nut when a torque exceeding a predetermined value is applied, wherein the foldable part is configured to prohibit rotation between the nut and bolt at an angular resolution not more than 360 degrees divided by twice the number of the grooves.