Introduction to GD&T

Geometric Dimensioning & Tolerancing (GD&T) is a symbolic language—standardized by ASME Y14.5 and similar ISO standards—used on engineering drawings and 3D models to precisely communicate allowable geometric variation. It defines the nominal (perfect) geometry of parts and assemblies, as well as their permissible size, form, orientation, and location deviations. GD&T makes design intention explicit, ensuring parts will work together as intended even with slight manufacturing variability