Though many people assume that casters and wheels are the same, they are actually quite different. A caster is made up of various components, including a wheel. A wheel is simply a round object that rolls and it rotates on an axle or shaft that passes through the center of the wheel. When a wheel is installed into a frame it becomes a caster. The frame is called a caster bracket, rig, or fork. There are rigid and swivel frames, therefore when a wheel is installed into one of these frames they become a rigid caster or swivel caster, respectively. The frame is then attached to the base of a piece of furniture or object; e.g. office chairs, shopping carts, etc.