Which term is not the 3-point reference system?

• A. K- hole
• B. Datum A
• C. Datum B
• D. Datum C

Answer: (A)

The main idea is the three-point reference system used in GD&T, where three datums establish a complete reference frame for measurements. Datum A, Datum B, and Datum C are the recognized datum features that define the primary, secondary, and tertiary references—giving you the X, Y, and Z directions and the orientation needed to locate any feature relative to a standard frame.

K-hole is not part of that set. It refers to a hole feature by name, but it does not itself designate a datum used to establish the full three-axis reference. Only Datum A, Datum B, and Datum C provide the complete three-point reference frame, so K-hole is not included in the 3-point system.