| 摘要 |
<p>The building prop contains an internal shaft which slides in an outer sleeve and incorporates a casing, the upper part of which is shaped as a truncated cone and the lower part of which is threaded onto the end of the outer sleeve. The upper part of the casing contains ball-bearings which are releasably located into grooves on the internal shaft by screwing the lower part of the casing upwards. This locks the internal shaft and the sleeve in the desired relative position.</p> |
