| 摘要 |
A crossmember defines guide surfaces to receive a leg tip. Preferably a screw, cam or lever applies nonimpulse force to wedge the tip against the surfaces. The tip is preferably unthreaded, exclusively noncircular in at least external cross-section, and very generally aligned with the leg axis. Preferably the screw or the like pulls the tip length-wise into the crossmember without rotating or threading the tip into the surfaces, and also retains the tip wedged in place. Also preferably a notch or analogous traction feature is formed in the leg or crossmember, and the screw (distinct from the tip) threaded to the other. The screw engages the notch to force the tip into the crossmember. Further preferably the crossmember includes at least two interfitted cross-pieces cooperating to define the guide surfaces; the leg has a segment with transverse dimension of at least 2 or 3 cm and long dimension many times that, and the crossmember is in essence stationary and generally horizontally extended, for supporting at least a person or comparable weight.
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