Abstract: A caster includes a base carrying a rotation shaft and forming a pivotal joint seat. Wheels are rotatably mounted to the rotation shaft. Each wheel has an inside surface that is recessed to form an inner rim. A brake arm has a first end rotatably coupled to the pivotal joint seat and a second end forming a brake pawl extending into the inner rims of the wheels. A spring is arranged between the brake arm and the base so that the spring normally biases the brake pawl to depress against the inner rims of the wheels to brake the wheels. A release knob is rotatably mounted to the base and forms a cam section positionable against the brake arm. The cam section, when rotated by the release knob, drives the brake arm backward to release the brake pawl from the wheels, allowing the wheels to freely rotate.

Abstract: A knockdown shelf structure includes multiple unit board members, each of which forms first jointing portions and second jointing portions, wherein each first jointing portions is engageable with a corresponding one of the second jointing portions of another unit board member so as to joint and securely couple these two unit board members to form a large span of support board by jointing a large number of unit board members together and wherein each unit board member has a bottom forming third jointing portions; and multiple elevating members, each of which has a top rim structured to be jointable to each of the third jointing portions of the unit board member so as to elevate the unit board member upward, whereby a shelf structure for supporting articles thereon is formed by assembling the unit board members and the elevating members together.