# Category: GD&T Symbol Rules and Examples

Articles related to GD&T symbol rules and walk-through examples of GD&T Symbols and their uses

## Envelope Requirement (E Symbol) – ISO Only

by Jason Richter on March 21, 2022.

The Envelope Requirement Symbol is used on ISO drawings to declare that size is to control form with respect to perfect form at MMC.

## Independency

by Jason Richter on March 9, 2022.

The Independency Symbol is used on drawings to declare that the requirement for perfect form at MMC or LMC is removed and the form tolerance may be larger than the size tolerance. This symbol only exists in the ASME Y14.5 standards, not the ISO GPS standards.

## GD&T Rule #1: Envelope Principle

by Jason Richter on March 3, 2022.

GD&T Rule #1, also known as the Envelope principle, states that the form of a regular feature of size is controlled by its “limits of size." Limits of size, or otherwise known as size tolerances, can be seen in many forms. A few of them are symmetric, unilateral, and bilateral.

## Unequally Disposed Profile

by Jason Richter on February 17, 2022.

The unequally disposed profile tolerance symbol is used to apply unilateral or unequal tolerance zones to a profile of a part.

## Circularity – The Tolerance Zone

by Brandon John on June 22, 2021.

There can be a lot of confusion when dealing with circularity – especially when identifying the tolerance zone compared to how Rule #1 of Geometric Dimensioning and Tolerancing controls it.  In this video, we provide...

## Position vs. Symmetry – Relative to a Datum Axis

by GD&T Basics on May 24, 2021.

This video is in response to a question that we received on our question line from Alex.  His question is as follows: “Is there a best-practice way to use Position (instead of Symmetry) to control...

## Virtual Condition – Does it apply at RFS?

by GD&T Basics on May 5, 2021.

In this question line video, Brandon discusses Virtual Condition and whether it can apply at Regardless of Feature Size (RFS). What is Virtual Condition (VC)? When a feature is controlled with the Maximum Material Condition...

## Profile of a Surface – Unilateral vs. Bilateral

by GD&T Basics on April 12, 2021.

What is the difference between unilateral and bilateral tolerance in a profile of a surface callout? In this post, Brandon explains the difference and gives examples of how they are used.     Profile of...

## Profile of a Line Tolerance Zone

by GD&T Basics on April 6, 2021.

This video is in response to a question that we received on our question line from Amar. Amar’s question is as follows: “If we are given a BASIC radius of 10mm, and on the radius,...

## Position – Controlling Threads on Features

by GD&T Basics on February 14, 2021.

This video is in response to a question that we received on our question line from Tim. Tim’s question is as follows: “We tend to use true position on threaded holes.  Is this valid?  If...

## Parallelism Feature of Size – Rules for DRF

by GD&T Basics on February 14, 2021.

This video is in response to a question that we received on our question line from Jamee.  Jamee’s question is as follows: “For parallelism of a circular feature of size (axis) can you use two...

## Cylindricity – Can you use Material Modifiers?

by GD&T Basics on February 14, 2021.

This video is in response to a question that we received on our question line from Lokesh.  Lokesh asked us if a material modifier can be used with cylindricity.  Geometric Dimensioning and Tolerancing modifiers are...

## Parallelism – Can you Reference 3 Datums?

by GD&T Basics on February 12, 2021.

This video is in response to a question that we received on our question line from Ignacio.  Ignacio asked us if it is a bad practice to reference three datums in a single drawing callout...

## Flatness – Surface vs. Feature of Size

by GD&T Basics on February 12, 2021.

In this video, Brandon discusses the difference between measuring Flatness of a Surface and Flatness of a Feature of Size (FOS). Flatness of a Surface Surface flatness is the type of flatness that most people...

## Composite Position vs Multiple Single Segment Tolerances

by Brandon John on December 19, 2020.

In this video, Brandon compares a Composite Feature Control Frame and a Multiple Single Segment Feature Control Frame to show the effect of each on Position tolerance. What is a Composite Feature Control Frame?  A...

## Position Tolerance and Basic Dimensions

by Seth Elder on November 12, 2020.

The video below is in response to a question that we received on our question line from Ash.   The question is as follows: “I regularly see drawings where spacing between a pair of holes is...

## Using Runout to Measure Concentricity

by Seth Elder on October 29, 2020.

The video below is in response to a question that we received on our question line from Jeff.   Jeff asked us if concentricity is always equal to half of the runout value.  ASME Y14.5 defines...

## Unilateral Tolerance and Bilateral Tolerance

by Seth Elder on October 12, 2020.

In this article, we explain the differences between bilateral, unilateral, and unequally disposed tolerances. What is a Tolerance? Tolerances on technical drawings communicate the amount of variation permitted from a target dimension.  The allowable variation...