What is a datum feature in GD&T?

• A. A feature used to establish a reference frame for measurement
• B. A tolerance value
• C. A type of fastener
• D. A machine tool setting

Answer: (A)

A datum feature is the physical feature on a part that provides the reference used to build the datum reference frame for measurement. In GD&T, measurements are interpreted relative to this frame, which is defined by one or more datum features (often a primary, secondary, and tertiary). These features—such as a flat surface, a cylindrical bore, or the axis of a hole—give a stable plane or axis from which position and orientation are measured. It’s not a tolerance value, a fastener, or a machine setting; it’s the actual part feature that establishes how the part is located in space during inspection.