Total runout is a 3D surface to axis control. It creates one tolerance zone that all surface elements must lie within simultaneously. When applied to a cylindrical feature, the tolerance zone is the radial separation between two cylinders coaxial with the datum axis. This controls 3D form (cylindricity), orientation and location to the datum axis. It does not control size, and therefore requires a separate size tolerance.

Circular runout is a 2D surface to axis control. It creates a series of 2D tolerance zones that apply independently. When applied to a cylindrical feature, each tolerance zone is the radial separation between two circles concentric with the datum axis. This controls 2D form (circularity), orientation and location to the datum axis. It does not control straightness, taper, or size, and therefore requires a separate size tolerance.