What is a symmetry tolerance?

• A. A tolerance for angular orientation
• B. Tolerances for overall size
• C. A tolerance that constrains the distribution of features about a datum plane or axis to be symmetric
• D. A tolerance for roundness

Answer: (D)

Symmetry tolerance controls how a group of features is distributed relative to a central reference, such as a datum plane or datum axis, so that the features are balanced on opposite sides of that reference. It defines a tolerance zone that is symmetric about the chosen plane or axis, meaning the distances of the features from the reference must be within a range that mirrors on both sides. This is especially useful for patterns or assemblies where the overall balance and centering of features matter, like a circular hole pattern around a central axis or mating features that must be evenly spaced.

It’s not about how large a single feature is (that would be a size tolerance), nor about the orientation of features (orientation or angular tolerances), nor about the roundness of a single element (a form tolerance for roundness). The key idea is ensuring the group of features is distributed symmetrically around a central reference.