| 摘要 |
The drum of a hoisting apparatus is axially shifted to frictionally engage a driving plate. The drum is shifted by rotating an adjacent, first disc about the drum axis relative to a coaxial stationary disc. Each of the discs has three holes of a particular configuration to define three cooperative pairs of holes. Each cooperative pair of holes receives a dowel of predetermined length so that rotation of the first disc causes the dowel to react against the discs and shift the first disc and drum away from the stationary disc and into frictional driving engagement with the driving plate.
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