What is the role of a datum feature symbol in GD&T?

• A. It indicates a datum plane to be used in measurements.
• B. It identifies the surface or feature used to establish a datum.
• C. It specifies a manufacturing step.
• D. It designates a measurement unit.

Answer: (B)

The datum feature symbol is about naming the physical surface or feature on the part that will establish a datum for measuring and locating other features. In GD&T, a datum is a theoretical reference plane, axis, or point derived from actual features of size or form on the part. The symbol attached to a feature points to that feature as the one used to define the datum, whether it’s a machined flat surface, a cylindrical surface, a hole axis, or another identifiable feature. This designation is what links the datum reference frame to the real part so measurements and tolerances can be applied consistently.

It’s not a label for a measurement plane by itself, nor is it a directive about manufacturing steps or units of measure. Those aspects are not what the datum feature symbol conveys.