Casters are a general term, including movable casters, fixed casters and movable brake casters. Movable casters are also known as universal wheels, whose structure allows 360 degrees of rotation; Fixed casters are also called directional casters. They have no rotating structure and cannot rotate. Usually, the two casters are used together. For example, the structure of the trolley is two directional wheels at the front, and two universal wheels at the back near the handrail. Casters are made of various materials, such as pp casters, PVC casters, PU casters, cast iron casters, nylon casters, TPR casters, iron core nylon casters, iron core PU casters, etc.