A free-wheel hub transmission mechanism which includes a threaded axle coupled to the seat stays of a bicycle, a hub barrel fastened to the free-wheel spokes of the bicycle and disposed around the threaded axle, a driving barrel sleeved onto the threaded axle and having one end inserted into the hub barrel and an opposite end fastened to the free-sprocket of the bicycle, a coupling socket mounted within the hub barrel around the threaded axle, a conical spring mounted within the hub barrel around the coupling socket, a conical bushing and a cup mounted within the hub barrel to stop the conical spring inside the hub barrel, a plurality of ball bearings mounted around the threaded axle, and two lock nuts respectively threaded onto two opposite ends of the threaded axle, wherein the coupling socket is forced forwards into engagement with an inside annular flange of the hub barrel, causing the threaded axle and the hub barrel to be turned with the driving barrel when the driving barrel is rotated clockwise by the free-sprocket of the bicycle; the coupling socket is disengaged from the inside annular flange of the hub barrel, causing the driving barrel to run idle when the free-sprocket of the bicycle is rotated counter-clockwise.
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