Editor's note: The original version of this “classic” article by William Tandler first appeared in Quality Digest media in June 2008 and was based on the ASME Y14.5 1994 standard. Updated here to address the ASME Y14.5 2009 standard, it is an alphabetically organized primer of the terms that define GD&T, and is extraordinarily valuable as a means to replace common “interpretations” of GD&T with uniquely clear statements of its intent.

W hen dealing with geometric dimensioning and tolerancing (GD&T), it soon becomes evident that GD&T is a word- and concept-rich subject. And so it must be, because it deals with two very complex worlds—the code-defined, perfect and imaginary world of GD&T itself, and the imperfect real world of actual parts, along with their associated manufacturing, inspection, and assembly processes.

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