| 摘要 |
A pump jack for traveling up and down a pole includes a frame member and upper and lower shackles supported on the frame member. A pump arm is coupled to the pump jack and is operated for alternatively gripping the pole by the upper and lower shackles. The upper shackle has a helical rod which is cranked by a handle to roll along the surface of the pole. To prevent an accidental rolling of the helical rod and thus slipping of the pump jack down the pole, and anti-spin friction device including a rubber disc and a bolt acting thereon, is provided on the end of the helical rod opposite to that which carries the handle.
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