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GD&T Week 2 – Geometric Dimension & Tolerance (GD&T)

by | Aug 30, 2019 | GDT | 0 comments

Essential Question #1

Do you want to learn a clear and concise standard for illustrating tolerances on industrial prints/plans/blueprints?


This blog post will help you learn what GD&T is and how to use it to design accurate parts which can be machined within tolerance.

Essential Question #2

Do you want to learn a drafting standard that is accepted throughout the manufacturing world?

Purpose of GD&T

“Geometric dimensioning and tolerancing (GD&T) is a standardized language used to communicate manufacturing tolerances on prints/plans. GD&T uses symbols to specify exact limits on variation. As a general rule, GD&T is applied according to ASME Y14.5-2009 (revision of ASME Y14.5-1994).” (Hammer p. 172)

Types of Variation

“The parts described on two-dimensional manufacturing prints are three-dimensional objects. Features on three-dimensional objects have up to four different types of variation from their ‘ideal’ design:

  • Size
  • Location
  • Orientation
  • Form or Shape

GD&T does not replace conventional forms of tolerances; rather it supplements them. Conventional, or ‘plus-or-minus,’ tolerances are effective at describing limits on allowable variation for sizes, but when they are applied to locate features or to orient features, there is often ambiguity. GD&T eliminates this ambiguity. Furthermore, the shapes (forms) of surfaces are not controlled by conventional tolerancing. (Hammer p. 173)


  1. [CNC Cookbook] РGD&T: Geometric Dimensioning and Tolerancing Training
  2. [Hammer] – Hammer’s Blueprint Reading Basics, 4th Edition by Charles A. Gillis. Publisher Industrial Press Inc.
  3. [Olivo] – Blueprint Reading and Technical Sketching for Industry by Thomas P. Olivo. Publisher Nelson Canada. (Olivo)
  4. [Sealed Source] – Blueprint Reading –



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