| 摘要 |
A flange section 12b protruding in a radial direction of a ball screw shaft 6a is formed at a lower end portion of the ball screw shaft 6a, and a protrusion stopper 12a which abuts on the flange section 12b to prevent the ball screw shaft 6a from protruding out of the rod 7 is formed in a hollow section of the rod 7. On the lower side of the hollow section of the rod 7, there is formed a retraction stopper 13a which abuts on a lower end portion 13b of the ball screw shaft 6a to limit the refraction of the rod 7.
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