Circular run-out is a unique geometrical tolerance. It can be a composite form control relating two or more characteristics, and it requires a practical test where the part is rotated through 360° about its own axis.
The results of this test may include errors of other characteristics such as circularity, concentricity, perpendicularity, or flatness, but the test cannot discriminate between them. It should therefore not be called for where the design function of the part necessitates that the other characteristics are to be controlled separately. The sum of any of these errors will be contained within the specified circular run-out tolerance value. The tolerance value is equal to the full indicator movement of a fixed point measured during one revolution of the component about its axis, without axial movement. Circular run-out is measured in the direction specified by the arrow at the end of the leader line which points to the toleranced feature. It must always be measured regardless of feature size, and it is convenient for practical purposes to establish the datum as the diameter(s) from which measurement is to be made, if true centres have not been utilized in manufacturing the part.
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