Which of the following statements best describes a datum feature?

• A. A surface, axis, or point used to establish a datum.
• B. A feature that has no dimension effect.
• C. A target used to measure color.
• D. A geometric tolerance symbol.

Answer: (A)

Datums create the reference frame for locating and orienting features on a part in GD&T. A datum feature is the physical feature that is used to establish that datum, and it can be a surface, an axis, or a point on the part. This definition directly captures why datums matter: they define where the origin and orientation of the part come from, which governs how all tolerance zones are measured and interpreted. The other ideas don’t fit because color targets and general geometric tolerance symbols aren’t datum features, and describing a datum feature as having no dimension effect isn’t accurate since its geometry is what establishes the datum itself.