Engineering · GD&T
Circular runout.
A composite tolerance for rotating features. As the part rotates about a datum axis, a dial indicator at any single cross-section must stay within the tolerance value (full indicator movement, FIM). Captures both circularity and coaxiality at that section in one number.
01 · Definition
Indicator at one 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 single cross-section of the toleranced surface, and rotating the part 360°. The total indicator movement (FIM) must stay within the tolerance value.
The result captures both at-section circularity and coaxiality (radial offset of the axis from the datum axis) at that single cross-section. It does not capture taper, axial bowing, or runout at other sections — those would require multiple inspection points or total runout.
02 · FCF and example
0.002 circular runout to A.
A bearing journal with ↗ 0.002 A means at any single cross-section along the journal, the dial indicator reads no more than 0.002″ FIM as the part rotates. Different sections may give different readings; each section is independently bounded.
Inspection: between centers on a roundness machine, or in a chuck on a CMM with rotational fixturing. The dial indicator (or probe) reads out the at-section runout directly.
03 · When to use
Picking circular vs total.
- Circular runout when only one cross-section matters (e.g., a single bearing journal, a face seal). Cheaper to specify and inspect.
- 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.
Keep exploring
Related tools & references
Full feature-control-frame symbol reference.
The full-surface version of circular runout.
Form component captured within a runout reading.
See how runout combines with size and location limits.
Choosing realistic runout callouts.
Technically reviewed by the True Precision Machining engineering team · Last reviewed June 2026
Standards referenced: ASME Y14.5-2018
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