Abstract: A central-controlled double wheel structure allows accurate performance in controlling the direction of movement of transporting devices when a braking block, a direction limiting member, and a toothed braking member are stably and properly intermeshed, thereby ensuring transporting devices to move in a preset straight direction. The double wheel structure has braking pads that are connected to bridging plates which are in turn connected to a connecting seat, and positioning of the braking pads is controlled by the upward or downward movement of the connecting seat as the bridging plates act as a lever structure with the axial rod as the axis. Further, the serrated cogging ends of the braking pads may intermesh into the cogging teeth of the wheel bodies to effectively stop the movement of transporting devices without subjecting the braking pads and the wheel bodies to extensive wearing.

Abstract: A castor includes a wheel frame, a roller, an elastic locating plate, a mandrel, a locating disk, a braking disk, a mounting tube, an elastic member, a control bar, two screw members, an adjusting member, and a connecting unit. Thus, the distance between the braking disk and the roller can be adjusted easily and quickly according to the user's requirement, thereby facilitating the user braking the roller. In addition, when the wall thickness of the roller is reduced due to rubbing or wearing, the distance between the braking disk and the roller can be adjusted to fit the wall thickness of the roller, thereby keeping the braking effect of the braking disk to the optimum.