Editing Caster (section)

== Other related wheels ==
There are four main classifications of wheels:
* A '''standard wheel''' has a center rotating hub (or bearing) and a compliant material on its outer side.
* A '''caster''' is a wheel mounted to a fork, with an optional, additional offset steering joint.
* An '''omnidirectional wheel''' ([[Mecanum wheel]], [[Omni wheel]], or Swedish wheel) is made of a large central hub with many additional smaller wheels mounted along the perimeter such that their axes are perpendicular to the central wheel. The central wheel can rotate around its axis like traditional wheels, but the smaller wheels can also enable movement perpendicular to the central axis.
* A '''spherical wheel''' is omnidirectional and is generally a spherical ball mounted inside a restraining fixture. An example is a [[ball transfer unit]].