Look around caster and wheels are every where... Hospitals, grocery stores, offices, industrial plants, delivery and warehouse just to name a few. A caster (or castor) is an undriven, single, double, or compound wheel that is designed to be mounted to the bottom of a larger object, like a cart, chair or equipment, so as to enable that object to be easily moved. They are available in various sizes, and are commonly made of steel, rubber, plastic, nylon, aluminum, or stainless steel.
Casters are found in numerous applications, including shopping carts, office chairs, and material handling equipment. High capacity, heavy duty casters are used in many industrial applications, such as platform trucks, carts, assemblies, and tow lines in plants. Generally, casters operate well on smooth and flat surfaces.
Rigid Casters: A wheel mounted to a stationary fork with an axle and nut that allows the cart or equipment to roll but will restrict lateral movement.
Swivel Casters: Similar to the rigid in that it is a wheel mounted to a fork, but the swivel will have a pivot to allow the wheel to rotate freely to help with movement and steering.
Locking Casters: Locking casters are usually but not always swivel. These casters are equipped with a brake mechanism to prevent the wheel from rolling when activated.