| 摘要 |
PURPOSE:To prevent a rotation toward loosening even if axial force drops due to a rapid change in temperature by forming an escaping groove in a direction reverse to a tilting direction of a thread and slantly tilted to an axial line and forming this part of the thread with a gentle forward side, a standing slope at a retreating side and a planer bottom. CONSTITUTION:An escaping groove 6 having an acute lead angle to an axial line in a direction opposite to a tilting direction is formed on a thread 4 with an asymmetrical cross section. This escaping groove 6 is formed of a gently tilting forward slope 6a, a retreating side slope 6b approximately perpendicular to a peripheral face of a screw axis and a planer bottom 6c between them. Therefore, when the screw is to be driven into a plastic material, a female screw can be smoothly formed on a peripheral wall of a prepared hole so that a rotation toward a direction of loosening can be prevented even if axial force drops due to a change in temperature. |
