How does a true position tolerance differ from a basic dimension, and how is it applied in a feature control frame?

• A. A basic dimension indicates an exact location/size not directly toleranced; the true position tolerance governs allowable deviation from that true position, placed in a feature control frame.
• B. A basic dimension indicates an exact location/size not directly toleranced.
• C. The true position tolerance defines the size of a hole.
• D. A basic dimension provides material finish.

Answer: (B)

A basic dimension marks an exact, theoretical location or size that is not directly toleranced. To actually control that location, a true position tolerance is defined, which creates a tolerance zone around the true position. That tolerance is then applied in a feature control frame attached to the feature, specifying the positional tolerance value (and any datum references). In practice, the basic dimension pinpoints where the feature should be, while the true position tolerance in the frame limits how far the actual feature’s axis can deviate from that pinpointed position, relative to the referenced datums.