| 摘要 |
The jack consists of two or more separate tubular members (1,2,3) with meshing threaded surfaces of different dimensions which enable the clearances between the threads to be adjusted, wedging or releasing the members in relation to one another. When the jack has two members, one of them acts as a screw and the other as a nut, and when it has more than two members at least one of them fulfils both functions. The variations in the thread dimensions can be in the base (6), sides (7) or head (8) of the thread surfaces, and the tubular members of the jack can be rotated manually by a bar or connected to a drive motor.
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