| 摘要 |
A propulsion unit for span scaffolds having vertical castered columns at the four corners thereof. The propulsion unit includes a first elongated frame member extending between the columns on one side of the scaffold, a second elongated frame member extending between the columns on the other side of the scaffold, and a third, wheeled, frame member extending crosswise between the first and second frame members, the third frame member being mounted on the first and second frame members for limited free vertical movement relative thereto.
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