The GD&T Runout symbol specifies the tolerance for a surface of revolution type feature indicating how much variation the surface is allowed to have during this 360-degree rotation. To specify the fluctuation limits of a feature when a part of it is rotated 360 degrees around the datum axis, we use the runout tolerance. The variation measured during the rotation must be within the specified range.
Runout is a GD&T symbol used when you need to have control on a rotating part, though there is no prohibition of its use on non-rotating parts. This runout and its 3D components are commonly used for parts like drills, gears, shafts, axles, and other circular machine moving parts around the automotive and other industries. This tolerance is an important characteristic to consider when oscillations or vibration of a high-speed rotating part can cause frictional losses as well as wear and tear of the machinery parts.