Caster

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 (the "vehicle") so as to enable that object to be easily moved. They are available in various sizes, and are commonly made of 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.

Types

Casters may be fixed to roll along a straight line path, or mounted on a pivot or pintle such that the wheel will automatically align itself to the direction of travel.

Rigid casters

A basic, rigid caster consists of a wheel mounted to a stationary fork. The orientation of the fork, which is fixed relative to the vehicle, is determined when the caster is mounted to the vehicle. An example of this is the wheels found at the rear of a shopping cart in North America. Rigid casters tend to restrict vehicle motion so that the vehicle travels along a straight line.