Double speed chain is a roller conveyor chain, on the conveyor line, the moving speed of the chain remains the same, but the tool and workpiece placed on the chain can be transported in accordance with the user's requirements to control the moving speed, stop the movement in the position that needs to stay, by the operator to carry out various assembly operations, and then make the workpiece continue to move forward after the completion of the above operation. Therefore, the double speed conveyor chain is also known as the controlled rhythm conveyor chain, the free rhythm conveyor chain, the double speed chain, the differential chain, the differential chain, and the engineering habit is called the double speed chain.