What Is a Runout?

Runout is a GD&T tolerance that limits how much the surface of a round part varies as the part rotates 360° about a datum axis. Circular runout checks each cross-section on its own; total runout checks the whole surface at once. It is traditionally measured as full indicator movement (FIM) on a dial indicator.

In short: runout is the wobble you would see on an indicator while spinning the part on its functional axis — and the drawing says how much is allowed.

What Does Runout Mean in GD&T?

A runout tolerance relates a surface to a datum axis, usually established from the diameters the part actually runs on, such as bearing journals. Without a datum axis there is nothing to rotate about, so runout always references one.

Because it checks the real surface rather than a derived center, runout picks up several errors at once: the surface being off-center from the datum axis, tilted relative to it, or out of round. What it never controls is size — that stays with the diameter's own tolerance.

Up to the 2009 edition, ASME Y14.5 defined runout by the full indicator movement of a dial indicator on the surface while the part turns 360°. The 2018 edition describes the same tolerance zones geometrically, since Y14.5 is not an inspection standard, but how runout is applied and what it permits did not change.

Shops also use the word for spindle or tool runout — the wobble of a rotating cutter or chuck. That is the same idea applied to the machine rather than a callout on the part.

Circular Runout vs Total Runout

	Circular runout	Total runout
What it checks	Each circular cross-section, independently	The entire surface at once
Tolerance zone on a cylinder	Two coaxial circles at each cross-section	Two coaxial cylinders along the full length
Controls on a cylinder	Circularity and location/orientation to the datum axis	Circularity, straightness, taper and cylindricity, plus location/orientation
Controls on a face at 90° to the axis	Wobble of each circular element	Perpendicularity and flatness of the whole face
Indicator method	Indicator fixed at each section while the part rotates	Indicator also traverses along the surface while the part rotates

Runout vs Concentricity

Both aim at coaxial features, but concentricity checked only the midpoints of a feature against the datum axis and ignored its form. ASME Y14.5-2018 removed concentricity and lists circular runout, total runout, position and profile as the ways to control coaxial features. Runout is usually the easiest of those to verify on the shop floor.

How to Specify Runout

• Pick datum features the part actually runs on in assembly — two bearing journals, or a face plus a diameter — so the inspection setup matches function.
• Use circular runout where each section just needs to run true, such as a seal diameter; use total runout where the whole surface must be straight and true, such as a long bearing seat.
• Keep the runout tolerance tighter than the size tolerance only where you really need form control; otherwise it adds inspection cost for little benefit.
• For turned parts that will be finish-machined, hold critical diameters and faces in one setup where possible, which keeps them on the same axis.

Turned parts such as shafts, bushings and pins are produced by CNC machining at NICE Rapid, with critical dimensions verified by CMM or manual gauging.

Frequently Asked Questions

What is runout in GD&T?

It is a tolerance that limits how much a surface varies as the part rotates 360° about a datum axis. It controls the surface's location, orientation and form relative to that axis, but not its size, and it is traditionally checked with a dial indicator.

What is the difference between circular and total runout?

Circular runout checks each circular cross-section separately, so it ignores taper and changes along the length. Total runout checks the whole surface at once, so it also controls straightness, taper and cylindricity — or flatness and perpendicularity on a face.

What is the difference between runout and concentricity?

Runout checks the actual surface as the part rotates, so it also catches out-of-roundness. Concentricity checked only the midpoints of the feature and ignored form. Concentricity was removed in ASME Y14.5-2018, and runout is the usual replacement.

Related Services at NICE Rapid

• CNC Machining — CNC turning for axially symmetric parts, with tolerances to ±0.01 mm and CMM or manual gauging of critical dimensions.
• Rapid Prototyping — turned and milled prototypes in metal and plastic, with inspection records available on request for every order.
• Request a Quote — include your drawing with runout callouts and datums so the inspection setup is agreed with the quote.

Sources

1. US Patent 9,651,356 B1, Background — runout tolerance "controls the form, orientation, and location of a cylindrical part... as it rotates"; circular runout applies to cross-sections, total runout to the entire length; runout relates features "to a datum axis x during a full 360 degree rotation" — image-ppubs.uspto.gov
2. Tec-Ease, GD&T Symbol: Circular Runout (ASME Y14.5-2018 §12.2) — applies independently to each cross-section; previous editions defined runout by full indicator movement (FIM), 2018 defines the zones geometrically without changing their effect; on a perpendicular face it controls wobble — tec-ease.com
3. Tec-Ease, GD&T Symbol: Total Runout (ASME Y14.5-2018 §12.2) — controls every characteristic except size on a cylinder; circular runout ignores changes in size along the length; on a perpendicular face, total runout controls perpendicularity and flatness — tec-ease.com
4. Tec-Ease, GD&T Symbol: Concentricity (2018) — concentricity removed from the standard; coaxial features controlled by position, circular runout, total runout and profile — tec-ease.com
5. NASA Kennedy Space Center, KSC-GP-435 Vol. I Rev. H Chg. 1, Engineering Drawing Practices — positional tolerances and runout should be used instead of circularity, concentricity and cylindricity tolerancing — standards.nasa.gov