| 摘要 |
Two guide sleeves, made of a suitable synthetic material, are attached to a threaded bar (9) opposite each other, holding a helical spring (6) between them, which is supported by collars positioned at the outer edges of the sleeves. The tension of the spring (6) can be adjusted by rotating a nut towards the collar of one of the sleeves and moving the opposite sleeve against two stop nuts (21). The adjusting screw can be returned to its former position.
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