| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem that a hydraulic cylinder is arranged in parallel with an axle, parts around the axle become complicated and a large arrangement space is required around the axle as the axle is conventionally constituted to extend and contract by using the hydraulic cylinder. SOLUTION: A movable flange body 30 is constituted of a flange boss 35 to mount a wheel and a fixing boss 34 and a pressing boss 33 included in the flange boss 35, a screw body is constituted of a male screw body 26 and a female screw body 25 externally fitted on an axle, the female screw body is connected to the axle, and one end of the male screw body is held and fixed between the flange boss and the fixing boss in constitution free to change a tread by revolution of the screw body by arranging the movable flange body 30 on which a wheel 36 is fixed free to slide on the axle 22 and connecting the screw body 20 to the movable flange body.
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