How is a datum reference frame used to evaluate a pattern of holes?

• A. It defines the maximum material condition for the holes.
• B. It provides the orientation and location reference for verifying the relative position of the hole axes.
• C. It determines the physical size of holes.
• D. It records the material of the workpiece.

Answer: (B)

A datum reference frame provides the orientation and origin used to judge a pattern of holes. Built from three datum features on the part, it defines a primary, secondary, and tertiary reference that establishes how the part is located and oriented. When evaluating a hole pattern, the true position tolerance zones for the hole axes are defined relative to this frame, so you compare each hole’s axis to the datum reference frame to verify its position and alignment within the specified pattern. This frame is what anchors how the pattern is measured, ensuring the holes’ relative positions are consistent with the design intent. It doesn’t determine hole size or material—that’s handled by other specifications.