What You Need to Encode a GD&T Symbol

To encode a GD&T symbol, you construct a Feature Control Frame, which consists of a rectangle divided into compartments containing:

• Geometric Characteristic Symbol
• Tolerance value or description
• Modifiers
• Applicable Datum Feature references

The image below shows an example Feature Control Frame with modifiers.

Prior to creating the symbol, you need to have the appropriate Datum Features in the model.

The geometry to which a GD&T symbol is applied is usually called a "Feature". Features may be specified by:

• Directly selecting a part's faces
• Selecting an existing datum feature
• Selecting an existing Feature Control Frame in the structure tree or graphics window

After choosing a Characteristic Symbol and the geometry (usually called Features) to which the tolerance will apply, you will select the relevant Datum Feature references.

An exception is Form tolerances, which do not use Datum Feature references.

When you first create a GD&T symbol, the default Characteristic Symbol is Position. Once you choose a different symbol, that becomes the default until you select another one.

Characteristic Symbols are shown in the table below.

Tolerance Type	Symbols				Applied To
Form	Straightness	Flatness	Circularity	Cylindricity	Individual Features
Profile	Line	Surface			Individual or Related Features
Orientation	Angularity	Perpendicularity	Parallelism		Related Features
Location	Position	Concentricity	Symmetry		Related Features
Runout	Runout	Total Runout			Related Features

Once you have selected the Datum Feature references, you are put in placement mode where:

• In 3D, you choose an annotation plane and then place the symbol somewhere within that plane
• In a drawing you place the symbol somewhere in the sheet