Figure 3. Alternative ways of attaching planner datum symbols.

On the drawing, any feature (or FOS) can be identified as a datum. These datum features are identified by capital letters inside a box and is attached to a feature or FOS with a leader line and a triangle. These datum features are referenced in the feature control frames to identify one or more datums. Figure 3 shows alternative ways of selecting datum features. (next).

Figure 4. Alternative ways of attaching axis or center plane datum symbols.

Figure 4. shows the alternative ways of specification of axis or centerplane datums. Notice that the datum symbols are attached to either a cylindrical surface or an FOS. In this case datum is always the center-plane or the axis, and not the feature itself.

Note: When more than one datum references are made, the part must located with respect to mutually perpendicular simulated datum planes for tolerance measurement. (Top)