Cart replacement wheels are referred to as casters. Types of casters include dual wheel, leveling, plate and stem. Pneumatic and solid rubber casters are also available, as well as specialty and twin wheel casters. Casters are not only used for carts; they are often used on office chairs and equipment meant to mobilize heavy materials. They can be stationary or swivel, and they are made of plastic, stainless steel, rubber or aluminum. Casters can also be fitted with brakes.
Stationary, or rigid, casters have wheels that do not turn from side to side. Consequently, the object on wheels only moves in a straight line. Rigid casters are commonly used as the back wheels of a shopping cart.
Swivel casters have wheels with the ability to rotate in any direction. These are used on equipment meant to move heavy material and as the front wheels on a shopping cart. While moving in a straight line, swivel casters tend to operate parallel to the object. This eliminates the need for precise steering, while the caster's ability to rotate lets it turn smoothly.
Casters fitted with brakes and locks are usually swivel casters. These are commonly found in the medical world, particularly on stretchers and hospital beds.