| 摘要 |
An elongatable telescoping support, e.g. for use as a vehicle jack, comprises an outer prismatic tubular support and an inner prismatic tubular support telescopingly received in the outer support. A head is formed at the mouth of the outer support bar and has a guide surface inclined toward the outer support bar upon which a guide roller is shiftable. The guide roller is formed with a profiled portion adapted to grip a running surface of the inner support bar upon rotation of the guide roller to displace the inner bar out of the outer bar. According to the invention, rings at the end of the roller are received in the inclined windows which are formed in opposite walls of the prismatic head and a guide element is pivoted on this head and is urged, e.g. by a spring, in a direction tending to bias the roller inwardly and toward the outer support or bar. The guide element can be formed of a double-arm lever which can be actuated against the force of the spring to release the contoured portion of the roller from the running surface of the inner support bar and lift the roller along the surfaces of the guide slots to permit inward telescoping of the inner support member.
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