| 摘要 |
A ladder including upstanding opposite side rails and vertically spaced rungs extending and mounted between the side rails is provided. A pair of screw shafts extend along and are journalled from the side rails and elongated guides are mounted from and extend along the upper end portions of the side rails. A pair of followers are guidingly engaged with the guides for movement therealong and the screw shafts are threadedly engaged with the followers. The lower ends of the shafts include structure for inputing rotary torque thereto and the followers include laterally outwardly projecting arm portions disposed generally normal to a plane containing side rails of the ladder. The arm portions include underside downwardly projecting teeth spaced therealong and the inner base ends of the arms are pivotally mounted from the followers for angular displacement of the arms between outwardly projecting operational positions and inwardly retracted positions disposed closely adjacent, generally paralleling and projecting downwardly along the screw shafts.
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