GD&T Symbole

Geometric dimensioning and tolerancing (GD&T) symbols

GD&T is the engineering language for specifying part geometry and tolerances unambiguously. This reference covers the five categories of geometric controls as defined by ASME Y14.5 and ISO 1101 standards.

• Form Controls: Straightness, Flatness, Circularity (Roundness), Cylindricity. Control the shape of individual features independent of datums.
• Profile Controls: Profile of a Line, Profile of a Surface. Control complex surfaces. Can be used with or without datums. The most powerful GD&T control.
• Orientation Controls: Parallelism, Perpendicularity, Angularity. Control the orientation of features relative to datums. Always require at least one datum reference.
• Location Controls: Position (True Position), Concentricity, Symmetry. Control the location of features relative to datums. True Position is the most used GD&T symbol.
• Runout Controls: Circular Runout, Total Runout. Control rotating surfaces relative to a datum axis. Common for shafts, bearings, and rotating components.

How to use this GD&T Symbols Reference Guide

Use this reference to interpret GD&T symbols on engineering drawings. Form controls ensure the shape of individual features. Position (true position) is the most common location control for hole patterns. Profile of a surface is the most versatile control for complex 3D surfaces. When reading a drawing, first identify the datums, then the controls applied to each feature.