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CNCCookbook Beginner's Guide to GD&T: Symbols

 

Geometric Dimensioning and Tolerancing (GD&T) Symbol Quick Reference

 

Control Type

 

Characteristic Symbol Notes
Form Flatness GD&T Flatness Symbol

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

Datum reference is not allowed

Straightness GD&T Straightness Symbol
Circularity (Roundness) GD&T Cicularity (Roundess) Symbol

Controls form (shape) of size features only.

Datum reference is not allowed

Cylindricity GD&T Cylindricity Symbol

Orientation

No relation between features

Perpendicularity GD&T Perpendicularity Symbol

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 GD&T Parallelism Symbol
Angularity GD&T Angularity Symbol
Location
Position GD&T True Position Symbol Locates center points, axes and median planes for size features. Can also control orientation.
Profile of a Surface GD&T Surface Profile Symbol

Locates surfaces.

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

Profile of a Line GD&T Line Profile
Runout Total Runout GD&T Total Runout Symbol

Controls surface coaxiality

Can also control form and orientation of surfaces

Circular Runout GD&T Circular Runout Symbol
Location of derived median points. Concentricity GD&T Concentricity Symbol

Locates derived median points of a feature

Not common, consider position, runout, or profile instead

Symmetry GD&T Symmetry Symbol

 

Feature Control Frame 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

 

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

 

GD&T Table of Contents

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