Radial vs. Axial — What's the Difference?

Radial designs or movements occur in a direction extending from a common center. This term is often used in engineering and physics to describe components or forces that spread outwards from a central point, like the radii of a circle. For instance, radial tires have reinforcing structures radiating from the center. In contrast, axial refers to something related to or around an axis, a straight line around which an object rotates or is symmetrically arranged. An example is an axial fan, where the flow moves along the axis of the fan.

In the context of machinery, a radial bearing is a type of rolling-element bearing that carries loads perpendicular to the axis of rotation, whereas an axial bearing, also known as a thrust bearing, carries loads parallel to the axis. Radial bearings are used where radial loads are predominant, but axial bearings are preferred for handling axial loads.

In anatomy, radial often describes structures related to the radius bone or radiating from a specific point. For example, the radial artery runs along the radius bone in the forearm. Axial in anatomy refers to structures along the central axis of the body, like the axial skeleton, which includes the skull, spine, and rib cage.

Radial symmetry is a form seen in many organisms, like starfish, where body parts are arranged around a central axis. Axial symmetry, on the other hand, refers to symmetry around a single axis, as seen in the human body.

Radial and axial also describe directions of movement or force application. Radial movement moves outward from the center, while axial movement occurs along an axis. For instance, radial expansion in a pipe occurs outward from the center, while axial expansion occurs along the pipe’s length.