GD&T Symbols Reference Guide - CNCCookbook

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This is your convenient guide for Geometric Dimensioning and Tolerancing (GD&T) symbols.  Click on any link below to lean more about each GD&T symbol or concept. You can also download a PDF version of this information by clicking the button:

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Control Type

Characteristic

GD&T Symbol

Notes

Form

Flatness

Controls form (shape) of size and non-size features.

Datum reference is not allowed

Straightness

Circularity (Roundness)

Controls form (shape) of size features only.

Datum reference is not allowed

Cylindricity

Orientation

No relation between features

Perpendicularity

Controls orientation (tilt) of surfaces, axes, or median planes for size and non-size features.

Datum reference required.

Optional: Angularity symbol may be used for all orientation controls.

Parallelism

Angularity

Location

Position

Locates center points, axes and median planes for size features. Can also control orientation.  See also True Position.

Profile of a Surface

Locates surfaces by describing a tolerance zone around the surface or line.

Can also be used to control size, form, and orientation based on datum reference.

Profile of a Line

Runout

Total Runout

Controls surface coaxiality

Can also control form and orientation of surfaces

Circular Runout

Location of derived median points.

Concentricity

Locates derived median points of a feature

Not common, consider position, runout, or profile instead

Symmetry

Feature Control Frames: Modifiers

Symbol

Modifier

Notes

Free State

Only applies if part is otherwise restrained.

Least Material Condition (LMC)

Useful to maintain minimum wall thickness

Maximum Material Condition (MMC)

Provides bonus tolerance only for a feature of size

Projected Tolerance Zone

Useful on threaded holes for long studs

Regardless of Feature Size (RFS)

Not part of the 1994 standard

Tangent Plane

Useful for interfaces where form is not required

Unilateral

Appears in the 2009 version and refers to unequal profile distribution

A Feature Control Frame describes the conditions and tolerances of a geometric control on a part’s feature.

Notes:

"RFS" means regardless of feature size.  It simply means that whatever GD&T callout you make, it is controlled independently of the size dimension of the part.  RFS is the default condition of all geometric tolerances (by rule #2 of GD&T) and requires no callout.

These GD&T symbols are provided as a reference for CNCCookbook's free GD&T Tutorial. To learn what they mean, clicks the links, read on or check the Table of Contents for more information.

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