Geometric Dimensioning and Tolerancing (GD&T)

GD&T is the logical capability of specifying allowable geometric variation — form, orientation, location, runout — using the symbolic feature-control framework defined by ASME Y14.5 (US) and ISO GPS (international). It communicates design intent unambiguously to manufacturing, inspection, and supplier teams.

What it covers

• Form controls — flatness, straightness, circularity, cylindricity.
• Orientation controls — perpendicularity, parallelism, angularity.
• Location controls — position (with bonus tolerance), concentricity, symmetry.
• Profile and runout controls for complex surfaces and rotating features.
• Datum schemes and material-condition modifiers (MMC, LMC, RFS) tying features to inspection setups.

Relationships (see sidebar)

• Supports the Detailed Design, Quality Management, and CAM Manufacturing Planning processes.
• Implemented by CAD systems including Siemens NX, Dassault CATIA, SolidWorks, PTC Creo, and Autodesk Inventor.
• Feeds Tolerance Analysis and is delivered via PMI Annotations in MBD datasets.