| 摘要 |
A treadmill includes a base having two side rails and each side rail has a passage defined therethrough. A frame having two sides are connected between the two side rails and a running belt reeves around two ends of the frame. Two collars are respectively movably received in the two passages and each collar has two first spiral ramps located on different surfaces. Two pins movably respectively extend through the two collars and are fixed to the two sides of the frame. Two springs are mounted to the two pins and biased between the two side tails of the base and the two sides of the frame. Each pin has two second spiral ramps located on different surfaces of a head of each pin. The first spiral ramps are movably engaged with the second spiral ramps.
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