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6.4.3 Circularity (Roundness). Circularity is a condition of a surface where:

(a) for a feature other than a sphere, all points of the surface intersected by any plane perpendicular to an atis are equidistant from that axis;

(b) for a sphere, all points of the surface intersected by any plane passing through a common center are equidistant from that center.

6.4.3.1 Circularity Tolerance. A circularity tolerance specifies a tolerance zone bounded by two concentric circles within which each circular element of the surface must lie, and applies independently at any plane described in (a) and (b) above. See Figs

6-8 and 6-9. The circularity tolerance must be less than the size tolerance, except for those parts subject to free state variation. See para. 6.8.

NOTE: See ANSI B89.3.1 for further information on this subject.

6.4.4 Cylindricity. Cylindricity is a condition of a surface of revolution in which all points of the surface are equidistant from a common axis.

6.4.4.1 Cylindricity Tolerance. A cylindricity tolerance specifies a tolerance zone bounded by two concentric cylinders within which the surface must lie. In the case of cylindricity, unlike that of circularity, the tolerance applies simultaneously to both circular and longitudinal elements of the surface (the entire surface). See Fig. 6-10. The leader from the feature control frame may be directed to either view. The cylindricity tolerance must be less than the size tolerance.

NOTE: The cylindricity tolerance is a composite control of form that includes circularity, straightness. and taper of a cylindrical feanrrc.

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