Which tolerance requires a cylindrical tolerance zone coaxial with a datum axis?

• A. Concentricity.
• B. Perpendicularity.
• C. Angularity.
• D. Profile.

Answer: (A)

Concentricity checks how centered a feature’s axis is relative to a reference datum axis. When this tolerance is specified, the true axis of the cylindrical or spherical feature must lie inside a cylindrical tolerance zone that is coaxial with the datum axis. In other words, the axis can’t drift away from the datum axis beyond the stated amount because the zone around that datum axis defines the allowable deviation.

This is different from the others: perpendicularity constrains a surface to be at a right angle to a datum plane, angularity fixes a specific angle between axes, and profile controls the shape of a surface boundary rather than the alignment of centers.