This is the datum that must be constrained first when measuring the part. The letter corresponds to a feature somewhere on the part which will be marked with the same letter.

Primary Datum Feature Reference (if required) – If a datum is required, this is the main datum feature used for the GD&T control.

See the Modifiers section of the GD&T Symbols page for further clarification on these features.

Feature of Size or Tolerance Modifiers (if required) – This is where you call out any tolerance modifiers in the feature control frame.

The unit of measure is based on the drawing standard. Tolerance Value – The TOTAL tolerance of the geometric control.Diameter Symbol (if required) – If the geometric control is a diametrical tolerance, then the diameter symbol (Ø) will be in front of the tolerance value.See our page on GD&T symbols for a description of each symbol. Geometric Symbol – This is where your geometric control is specified.Leader Arrow – This arrow points to the feature that the geometric control is placed on.This information provides everything you need to determine how the geometrical tolerance needs to be interpreted and how to measure or determine if the part is in specification.

Datum references (if required by the GD&T symbol).Tolerance zone modifiers: material condition modifiers, projections….The feature control frame consists of four main pieces of information: A feature control frame is used in Geometric Dimensioning and Tolerancing to describe the conditions and tolerances of a geometric control on a part’s feature.

Gd&t symbol for flatness