Runout Tolerances: Circular and Total
Verified by rotation, always RFS
Runout is the only control verified by rotating the part about a datum axis while an indicator contacts the surface. Circular runout is checked at each circular element separately. Total runout sweeps the whole surface as the part rotates and the indicator traverses along it. Both require a datum axis, both apply to surfaces of revolution (cylinders, cones, faces), and neither accepts an MMC or LMC modifier - runout is always RFS.
Circular runout controls the location and form of individual circular elements. Because each element is judged on its own, coaxial taper and irregularities between elements can slip through: a perfectly round but conical surface coaxial with the datum axis reads essentially zero circular runout. Total runout controls form, orientation, location, and profile of the entire surface simultaneously, making it a tight combined control that catches taper and lobing.
Traps: adding MMC to runout, which is illegal; expecting runout to control size, which needs its own limits; applying runout to a feature that does not rotate about the datum axis; and forgetting that a face can be runout-toleranced, where it controls wobble and implicitly perpendicularity and flatness relative to the axis.
Worked example: a shaft of diameter 30 with circular runout 0.05 to datum A. Total indicator readings of 0.04, 0.03, and 0.06 at three axial stations mean the part fails - the 0.06 station exceeds the limit even though the others pass. Switching the callout to total runout would require every reading along the full traverse to stay within 0.05.