Abstract: An assembly of a brake disk and a hub includes an axle extending through a passage in the hub and a plurality of longitudinal ridges extend from each of the two ends of the axle. Each end of the axle has a threaded hole defined in an end surface thereof. The brake disk has a central hole and a plurality of notches defined in an inner periphery of the central hole so as to have protrusions located between the notches. The ridges are received in the notches and a bolt extends Through each of the protrusions and is threadedly engaged with the threaded hole in the ridge.

Abstract: A wheel shaft structure of a monocycle includes a wheel rim, and a shaft assembly mounted in a center of the wheel rim. The shaft assembly includes a wheel shaft passed through the wheel rim, two opposite single-direction bearings symmetrically mounted on the wheel shaft and received in the central hole of the wheel rim, and two opposite double-direction bearings symmetrically mounted on the wheel shaft and received in the central hole of the wheel rim.

Abstract: This is a structural improvement of pulley for bicycle, involving a pulley gear installed at one side of the joint where a center tube, a bearing and a single-direction flywheel are joined at the center of a rear wheel. Meshed on the pulley gear is a toothed belt. At the other end of the toothed belt is a motor spindle gear. Thereby, a battery providing power to drive the motor, the toothed belt, and the rear wheel to drive the bicycle forward.