High Quality Content by WIKIPEDIA articles! Geometric dimensioning and tolerancing (GD&T) is a quality control method for primary-generated three-dimensional solid models that explicitly describes nominal geometry and its allowable variation. It is an international code used by people who design tools and parts, to tell machinists and manufacturers what the proper dimensions of a given part must be. GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features. Geometric dimensioning and tolerancing specifications are used as follows: