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?
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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.

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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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Applications of GD&T (ASME Y14.5M-1994) - New! ASME Y14.5M-1994-2009 Update - New! ASME to ISO Standards Comparison Engineering Drawing Requirements - Exclusively from ETI! Executive Overview of GD&T - Exclusively from ETI! Functional Gaging and Measurement (Y14.5, Y14.5.1, Y14.43) - New! GD&T Advanced Concepts of GD&T (ASME Y14.5M-1994) GD&T Fundamentals (ASME Y14.5M-1994) GD&T Fundamentals (ASME Y14.5-2009) GD&T Fundamentals for Inspectors (ASME Y14.5M-1994) - New! GD&T Overview Workshop (ASME Y14.5M-1994) - Exclusively from ETI! ISO Geometrical Tolerancing - New! Solid Model Tolerancing: The ASME Y14.41 Standard - Exclusively from ETI! Statistical Tolerance Stacks - Exclusively from ETI! System Approach to Component Tolerancing - Exclusively from ETI! Tolerance Stacks (concept driven)