Chapter 3 Datums 113 The Center of a Pattern of Features as the Datum Axis The center of a pattern of features, such as the holes in the part shown in Example 3-42, can be specified as the datum axis when the datum feature symbol is placed under and attached to the middle of the feature control frame. In this application, the datum axis is the center of the holes as a group. This will be discussed further in Chapter 7 in regard to location tolerances. Datum center plane A Datum feature simulator Datum feature simulator Datum feature simulator of datum feature of datum feature of datum feature A A A Parallel planes at maximum Parallel planes at maximum Parallel planes at maximum separation (RMB) separation (RMB) separation (RMB) Part Datum feature A Datum feature simulator Example 3-41. Simulated datum center plane for an internal datum feature. Datum axis B Datum axis B Example 3-42. The datum axis at the center of a pattern of features as a group.