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GD&T Symbols

Because GD&T is such a precise language, it involves a great many symbols and terms. Here are some of the symbols that are involved in geometric dimensioning and tolerancing fundamentals with a short definition of each.

How many of these symbols and topics do you understand?
The GD&T Skills Survey is a free resource from ETI that measures how well an individual understands the correct application and interpretation of GD&T. The survey is designed to challenge your GD&T knowledge so you can understand what level of GD&T training you need.

The survey can be used by individuals or companies. The 25-question survey takes minutes to complete, and you gain a better understanding of what you know about GD&T and what you need to learn. Find out more.


Geometric Characteristic Symbols - There are 14 geometric characteristic symbols used in GD&T. They are used to describe size, location, orientation, and form.
Angularity - The condition of a surface, centerplane or axis being exactly at a specified angle
Circularity - A condition where all points of a surface of revolution, at any section perpendicular to a common axis, are equidistant from that axis.
Concentricity - The condition where the median points of all diametrically opposed elements of a cylinder (or a surface of revolution) are congruent with the axis of a datum feature.
Cylindricity - A condition of a surface of revolution in which all points of the surface are equidistant from a common axis. 

Flatness - The condition of a surface having all of its elements in one plane. 

Parallelism - The condition that results when a surface, axis or centerplane is exactly parallel to a datum.
Perpendicularity- The condition that results when a surface, axis, or centerplane is exactly 90° to a datum. 
Position - The zone within which the axis or center plane of a feature is permitted to vary from true (theoretically exact) position. 
Profile of a Line Control - A geometric tolerance that limits the amount of error for line elements relative to their true profile.
Profile of a Surface Control - A geometric tolerance that limits the amount of error a surface can have relative to its true profile.

Circular Runout - A composite control that affects the form, orientation, and location of circular elements of a part feature relative to a datum axis.

Straightness (Axis or Centerplane) - The condition where an axis is a straight line (or, in the case of a centerplane, each line element is a straight line). 
Symmetry - The condition where the median points of all opposed elements of two or more feature surfaces are congruent with the axis or centerplane of a datum feature. 
Total Runout - A composite control affecting the form, orientation, and location of all surface elements of a diameter (or surface) relative to a datum axis.

Carry the GD&T Ultimate Pocket Guide with you on the job.
It contains all these symbols, a glossary, and more.


GD&T Modifiers and Symbols
- There are many other modifiers and symbols used in geometric tolerancing. Here are a few:
All-Around Symbol - A circle placed on the bend of the leader line of a profile control.
Basic Dimension - A numerical value used to describe the theoretically exact size, true profile, orientation, or location of a feature or datum target.
Between Symbol - A double ended arrow that indicates the tolerance zone extends to include multiple surfaces.
Controlled Radius - A radius with no flats or reversals allowed. The symbol for a controlled radius is "CR."
Datum Feature - A part feature that contacts a datum. 
Datum Target - A symbol that describes the shape, size, and location of gage elements that are used to establish datum planes or axes.
Feature Control Frame - A rectangular box that is divided into compartments within which the geometric characteristic symbol, tolerance value, modifiers, and datum references are placed.
Least Material Condition - The condition in which a feature of size contains the least amount of material everywhere within the stated limits of size.
Maximum Material Condition - The condition in which a feature of size contains the maximum amount of material everywhere within the stated limits of size.
Projected Tolerance Zone - A tolerance zone that is projected above the part surface.
Radius - A straight line extending from the center of an arc or circle to its surface.

Read more about it—

Understanding how to apply and interpret GD&T correctly will help you:

  • Create clear, concise drawings
  • Improve product design
  • Create drawings that reduce controversy, guesswork, and assumptions throughout the manufacturing process
  • Effectively communicate or interpret design requirements for suppliers and manufacturing

Read more about GD&T and how it will help your organization save money through better communication and increased productivity:

GD&T Resources (Including technical papers that discuss GD&T)

What is GD&T?

A GD&T glossary

"The Tao of Tolerancing," by Alex Krulikowski (ETImail Volume 1, Issue 5)

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The Ultimate Pocket Guide on Geometric Dimensioning and Tolerancing is a handy reference tool in one convenient pocket-sized package. Carry it with you on the job and have a resource to all your GD&T questions at your fingertips. More info

 



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This file last modified 11/12/13