Reference

GD&T Symbols Reference

The 14 geometric characteristics of GD&T grouped into form, orientation, location, profile, and runout, with a plain-language note on what each one controls.

GD&T (geometric dimensioning and tolerancing) is a symbolic language, standardized in ASME Y14.5, for defining the allowable variation in a part's geometry: how flat, round, straight, oriented, and located its features must be. It replaces ambiguous plus/minus dimensions with controls tied to datums, so a part means the same thing to the designer, the machinist, and the inspector. The system has 14 geometric characteristics, grouped into five families.

The 14 geometric characteristics

Form controls need no datum; orientation, location, and runout controls all reference at least one datum. Profile can control form alone or, with datums, form, orientation, and location together.

Characteristic	Type	What it controls
Straightness	Form	How straight a line element or axis is; no datum
Flatness	Form	How flat a surface is between two parallel planes; no datum
Circularity (roundness)	Form	How round a cross-section is; no datum
Cylindricity	Form	Roundness and straightness of a whole cylinder; no datum
Perpendicularity	Orientation	A feature at 90 degrees to a datum
Angularity	Orientation	A feature at a specified angle to a datum
Parallelism	Orientation	A feature parallel to a datum
Position	Location	Location of a feature (usually a hole or axis) from datums
Concentricity	Location	Median points of a feature coaxial with a datum axis
Symmetry	Location	Median points of a feature symmetric about a datum plane
Profile of a line	Profile	A 2D cross-sectional contour within a tolerance band
Profile of a surface	Profile	A 3D surface within a tolerance band; can control form, orientation, and location
Circular runout	Runout	Wobble of a single cross-section about a datum axis
Total runout	Runout	Combined wobble and taper of a whole surface about a datum axis

Concentricity and symmetry were removed in ASME Y14.5-2018 (see below); older drawings and ISO practice still use them, so all 14 are listed.

The five families

Form (straightness, flatness, circularity, cylindricity) controls the shape of a single feature and never uses a datum. Orientation (perpendicularity, angularity, parallelism) controls the angle of a feature to a datum. Location (position, concentricity, symmetry) controls where a feature sits. Profile (profile of a line, profile of a surface) controls a contour against a true profile and is the most versatile control. Runout (circular runout, total runout) controls surfaces of revolution as the part spins about a datum axis. Position is by far the most used control for holes and mating features.

Concentricity and symmetry were removed in 2018

ASME Y14.5-2018 deleted concentricity and symmetry, leaving 12 active characteristics in the current standard. Both were hard and expensive to inspect because they rely on deriving median points, and in practice they were almost always better handled another way: position (often at maximum material condition), profile, or runout controls the same coaxial or symmetric relationships more clearly and more cheaply. They are still valid on drawings made to the 2009 or earlier editions and remain in ISO GD&T, which is why this reference keeps all 14. On new ASME Y14.5-2018 drawings, use position, profile, or runout instead.

Characteristics and grouping reflect ASME Y14.5. The 2009 edition defines all 14; the 2018 edition removed concentricity and symmetry, leaving 12. ISO GD&T (ISO 1101) uses a similar set. Confirm which standard and edition your drawing is built to.

On OpenSpindle

Frequently Asked Questions

What is GD&T?

GD&T (geometric dimensioning and tolerancing) is a symbolic language, standardized in ASME Y14.5, for defining the allowable variation in a part's geometry: form, orientation, location, profile, and runout. Tied to datums, it removes the ambiguity of plus/minus dimensions so the design, the shop, and inspection all read the part the same way.

How many GD&T symbols are there?

There are 14 geometric characteristics in ASME Y14.5: four form (straightness, flatness, circularity, cylindricity), three orientation (perpendicularity, angularity, parallelism), three location (position, concentricity, symmetry), two profile (line and surface), and two runout (circular and total). The 2018 edition removed concentricity and symmetry, leaving 12.

Which GD&T controls need a datum?

Form controls (straightness, flatness, circularity, cylindricity) never use a datum because they control a single feature's shape. Orientation, location, and runout controls always reference at least one datum. Profile can be used with or without datums depending on whether you are controlling form only or also orientation and location.

Why were concentricity and symmetry removed from ASME Y14.5-2018?

They were difficult and costly to inspect because they depend on deriving median points, and position, profile, or runout controls the same coaxial or symmetric relationships more clearly. ASME Y14.5-2018 removed both, leaving 12 characteristics. They remain valid on older-edition and ISO drawings, so replace them with position, profile, or runout on new ASME drawings.

Upload a drawing with your GD&T callouts and datums, and set a budget. We source shops equipped to hold and inspect them and bring back a best-match quote.

Get quotes for GD&T-toleranced parts