| 摘要 |
PROBLEM TO BE SOLVED: To make an engagement ratchet not easily break away from a securing groove. SOLUTION: An engagement structure ha of the engagement ratchet 29 is that the securing groove 21 extending back and upward is disposed at the front face of a supporting rail 16 and the engagement ratchet 29 facing back and upward is engaged with the securing groove 21. The upper surface of the securing groove 21 is formed into a convex circular face from the open end to the back end part and the upper surface of the engagement ratchet 29 is formed into a concave circular face with the same curvature of the convex circular face. COPYRIGHT: (C)2004,JPO&NCIPI
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