Casters generally include movable casters, fixed casters and movable brake casters. Movable casters are also what we call universal wheels. Its structure allows 360-degree rotation; fixed casters are also called directional casters, which have no rotating structure and cannot be rotated. Usually two kinds of casters are used in combination. For example, the structure of a trolley has two directional wheels at the front, and two universal wheels at the back, which are close to the push armrest. 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.