GD&T Symbols & Definitions Guide (ASME Y14.5) — Quick Reference

by

GD&T Reference Guide (ASME Y14.5)

Geometric Dimensioning and Tolerancing symbols and definitions.

1. FORM (No Datums)

Symbol Name & Definition
Straightness Symbol Straightness: 2D straightness of a line element.
Flatness Symbol Flatness: Surface must lie between two parallel planes.
Circularity Symbol Circularity: Roundness of a 2D cross-section.
Cylindricity Symbol Cylindricity: Roundness + Straightness of a 3D cylinder.

2. ORIENTATION (Datums Required)

Symbol Name & Definition
Perpendicularity Symbol Perpendicularity: 90° to datum (surface or axis).
Parallelism Symbol Parallelism: Equidistant to datum (surface or axis).
Angularity Symbol Angularity: Any specified angle to datum.

3. LOCATION (Datums Required)

Symbol Name & Definition
Position Symbol Position: Locates a feature relative to datum(s) within a 3D tolerance zone (True Position).
Concentricity Symbol Concentricity: Axis of one cylinder relative to datum axis.
Symmetry Symbol Symmetry: Feature median plane relative to datum median plane.

4. PROFILE (Datums Optional)

Symbol Name & Definition
Profile of a Line Symbol Profile of a Line: Controls a 2D profile (curve or straight) relative to a datum or basic dimensions.
Profile of a Surface Symbol Profile of a Surface: Controls a 3D profile (surface) relative to a datum or basic dimensions.

5. RUNOUT (Datums Required)

Symbol Name & Definition
Circular Runout Symbol Circular Runout: Controls combined circularity & coaxiality of a rotating feature.
Total Runout Symbol Total Runout: Controls combined cylindricity & coaxiality of a rotating feature.

6. DATUM FEATURES (Reference)

Symbol Name & Definition
Datum Feature Symbol Datum Feature Symbol: Designates a datum feature (e.g., surface, axis) used for measurements.
Datum Target Symbol Datum Target Symbol: Used when a datum feature is too large or irregular for a single datum feature symbol. Specifies specific points or areas on the datum.