| 摘要 |
<p>The slope angle (α) of the arcuate portion (32) of a fitting projection (20) is larger than the slope angle (β) of the arcuate portion (26) of a recess (16), and the axial intermediate portion of the fitting projection (20) is engaged with the opening edge of the recess (16) to transmit the tightening torque; therefore, compared with the case where α<β and the front end (20a) of the fitting projection (20) is engaged with the intermediate portion of the recess (16), the diameter of an engaging region (38) becomes larger, so that in the case of tightening with the same tightening torque, the force applied to the engaging region (38) becomes smaller in inverse proportion to the diameter. For this reason, local damage or deformation of the fitting projection (20) and recess (16) in the engaging region (38) is suppressed, or it becomes possible to satisfactorily tighten a small-diameter screw (10) with higher tightening torque. Further, if the force applied to the engaging region (38) becomes smaller, the component of force produced on the basis of the slope of the arcuate portion (32) in a direction of axial separation becomes smaller, thereby suppressing the come-out of a bit (18) rising up from the recess (16), stabilizing the tightened state of the small-diameter screw (10).</p> |
