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. 

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

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. 
GD&T Modifiers and Symbols  There are many other modifiers and symbols used in geometric tolerancing. Here are a few:

AllAround 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
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. 

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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