Which statement best describes circular runout versus total runout?

Which statement best describes circular runout versus total runout?

• A. Circular runout measures deviation around a single cross-section during rotation; total runout measures deviation over the entire rotation of the feature.
• B. Circular runout measures total length; total runout measures diameter variation.
• C. Circular runout applies to flatness; total runout to straightness.
• D. Circular runout is a size tolerance; total runout is a form tolerance.

Answer: (A)

Runout tolerances describe how far a surface deviates from ideal geometry as the part is rotated about a datum axis. Circular runout looks at a single cross-section: as you rotate the part, you compare that one plane of the surface to a true circle and record the deviation in that cross-section. Total runout, by contrast, evaluates the surface over the entire length of the feature during rotation, so any out-of-roundness anywhere along the feature is included in the tolerance. That’s why the best description is that circular runout measures deviation around a single cross-section during rotation, while total runout measures deviation over the entire rotation of the feature. The other statements mix up what is being measured (length or diameter), or unnecessarily tie runout to flatness/straightness or to size versus form.

Runout tolerances describe how far a surface deviates from ideal geometry as the part is rotated about a datum axis. Circular runout looks at a single cross-section: as you rotate the part, you compare that one plane of the surface to a true circle and record the deviation in that cross-section. Total runout, by contrast, evaluates the surface over the entire length of the feature during rotation, so any out-of-roundness anywhere along the feature is included in the tolerance. That’s why the best description is that circular runout measures deviation around a single cross-section during rotation, while total runout measures deviation over the entire rotation of the feature. The other statements mix up what is being measured (length or diameter), or unnecessarily tie runout to flatness/straightness or to size versus form.