I describe the 3 basic steps in applying GD&T from the ASME Y14.5-2009 Standard.

The following quotes are from Page IV of the ASME Y14.5-2009 Standard.

Step 1: “When applying GD&T the first consideration is to establish a datum reference frame based on the function of the part in the assembly with its mating parts.”

Step 2: “After the datum reference frame is established, the form of the primary datum feature is controlled, followed by the orientation and or location of the secondary and tertiary datum features.”

Step 3: “After the datum features are related relative to each other, the remaining features are controlled for orientation and location relative to the datum reference framework.”