Circular runout.

01 · Definition

Indicator at each section.

Circular runout is verified by mounting the part on its datum axis (between centers, in a chuck, or on a precision spindle), placing a dial indicator at a cross-section of the toleranced surface, and rotating the part 360°. The total indicator movement (FIM) at that section must stay within the tolerance value — and the requirement applies at every circular element along the surface, so the check is repeated at several sections.

Each reading captures both at-section circularity and coaxiality (radial offset of the axis from the datum axis) at that cross-section. Because every circular element is judged independently, circular runout does not control the surface as a whole — taper, axial bowing (straightness) and cylindricity are not limited. Those require total runout.

03 · When to use

Picking circular vs total.

• ▸Circular runout when each cross-section must run true but taper and straightness of the surface as a whole don’t matter (e.g., a bearing journal, a face seal). It still applies at every circular element along the feature, each independently; cheaper to inspect than total runout.
• ▸Total runout when the entire surface needs control as the part rotates (rotor surfaces, balanced shafts, sealing surfaces along their length).
• ▸Don’t use runout if there’s no datum axis — runout requires a rotation reference. For non-rotating features, use position or profile.
• ▸Runout is universal across ASME Y14.5 revisions — unlike concentricity and symmetry, runout is well-defined and universally inspected the same way.