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Should your company be using an addendum to the Y14.5 standard? Part 2 – Five Content Categories of an Addendum


This part of the article on addendums to Y14.5 covers the five categories typically found in an addendum.

Throughout this article where a number appears between square brackets, e.g. [xx], it refers to the paragraph or figure that is being modified from the ASME Y14.5-2009 standard.

There are five categories of content commonly found in corporate addendums. 

1. Allow the use of only one of several optional methods.
2. Change a default condition.
3. Clarify a concept, symbol, modifier, or definition for your companies' application.
4. Discourage/disallow the use of a concept, symbol, or modifier.
5. Document the use of a tolerancing practice that is not in the Y14.5  standard toolbox.

Examples of modifications in each content category are in the paragraphs below. Corporate addendums may include many or just a few modifications.  This article contains a few examples of modifications that are common in addendums.

The format of an addendum varies in each company. The format shown here may not be optimal for your company.

The examples in this article are not arranged in the sequence of a typical addendum. The examples are grouped by category.

The first category: Allow the use of only one of several optional methods. 

This content category is popular in addendums. Selecting an option when several practices are permitted in the Y14.5 standard is important because it helps to create consistent drawings and reduce confusion.

The list below contains a few examples of selecting an option from the Y14.5 standard.

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    The use of SI metric (mm units) is recommended [1.5]
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    Angular units shall be specified using decimal degrees [1.5.5]
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    Unless otherwise specified, all dimensions apply after heat treat and surface coatings [2.4.1]
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    Where the location of datum targets are defined with dimensions,  basic dimensions shall be used [4.24.7].

The second category: Change a default condition.

In most cases default conditions are not revised in an addendum; they are addressed on the face of a drawing.  What should be in an addendum is a list of which defaults should be overridden on your drawings and instructions on how to override them.

Changing a default can be beneficial because the default may not be the best for your company. For a list of common defaults in the Y14.5 standard, check out the blog article "Do you know which ASME Y14.5-2009 defaults apply to your drawings?")    Click here to read the defaults article

If the default conditions are not the same for all types of parts in your company, the addendum should show what parts should have defaults overridden and how to denote the override condition.

The advantage of revising standard defaults on the face of a drawing is that the requirement or condition is visible to the drawing users.

The third category: Clarify a concept, symbol, modifier, or definition for your companies application.

Clarifying concepts from the Y14.5 standard is important because it reduces confusion by providing additional explanation of items that are not fully explained in the standard.

The list below contains a few examples where clarifying a concept from the Y14.5 standard could be in an addendum.

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    Where the Independency symbol is applied to a size dimension of an external feature of size, and a form control is applied to one of the surfaces, its outer boundary of the feature of size shall be determined by the MMC of the feature of size plus the effects of the form control. [2.7.3]
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    A few terms that you may want to clarify with your addendum are: element, continuous feature, free state, and define what UOS means on a drawing and how to determine when is it overridden. [1.3]
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    Clarify whether surface texture is included in size tolerances and geometric tolerances. For a discussion that shows the different interpretations in industry check out the article "Survey results on the interpretation of the ASME Y14.5 standard"   Click here to read the article
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    How to designate and interpret a complex curve as a datum feature. [4.1]
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    Document the standards that apply to your drawings. The standards cited in this paragraph apply at the date shown. Any newer version shall not apply unless explicitly stated in this addendum. If a conflict exists between the text any of the standards cited and this addendum, the text of this addendum shall take precedence. [1.2]


Each ASME standard contains a paragraph citing a list of additional standards it invokes and provides a method to determine which standards are partially invoked.

However, many companies have difficulty understanding exactly which standards, and which versions apply to their drawings.

The fourth category: Discourage/disallow the use of a concept, symbol, or modifier.

Discouraging or disallowing the use of a symbol or concept is important because it reduces the number of tolerancing tools available for use on drawings. There are many tolerancing tools in the Y14.5 toolbox that are not needed for some types of parts. There are also tolerancing tools that are not used often.

There are subtle differences between some of the GD&T symbols. There are often discussions over which symbol is better for an application. The addendum focuses the discussions by disallowing or discouraging certain tolerancing tools leaving the tolerancing tools needed for defining your products.

Tolerancing tools can be disallowed for a variety of reasons. A few tolerance tools are overly restrictive for most applications or are not a good tool for your companies' applications. A few tolerancing tools that are only used in rare applications may be disallowed or discouraged to prevent their widespread use.

The list below contains a few examples of disallowing or discouraging a concept, symbol, or modifier.

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    The concentricity symbol shall not be used. [7.6]
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    The symmetry symbol shall not be used. [7.7.2]
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    The Statistical Tolerance modifying symbol shall not be used. (3.3.10)

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    The "alternative practice" to control parallel and perpendicular relationships shall not be used. [6.6]

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    Direct tolerancing (often referred to as plus and minus or limit tolerancing) methods shall not be used for location or orientation of features of size. [2.2]

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    The practice to override the degrees of freedom by reference of an order of precedence shall not be used. [4.22]

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    The method of specifying datum features at LMB shall not be used. [4.11.7]
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    The method of multiple LMB's shall not be used. [4.11.8]


Another area that I recommend companies to address is to discourage "extension of principle" on their drawings when a tolerance application is not in the Y14.5 standard or in their addendum. Even though the extended principle may make sense to the drawing creator, since its interpretation is not documented, it can be interpreted differently by drawing users.

The fifth category: Document the use of a tolerancing practice that is not in the Y14.5 standard toolbox.

Documenting the use of a symbol or concept that is not covered in the Y14.5 standard is important. It helps drawing users to have a consistent interpretation of the drawing requirements. If you add a new symbol or concept, it should be fully explained from a functional and inspection standpoint. 

The list below contains a few examples of tolerancing tools that are not in the Y14.5 standard but may be needed. In this section, only example topics are listed, the entire addendum text and figures to fully describe these items are too lengthy for this article.

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    A method to define a uniform Thickness/Gap Tolerance. (e.g. a wall thickness.).
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    How to designate a wedge as a datum feature.
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    When and how to document restraint conditions.
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    The Free-State modifier along with Restraint notes may be used on both non-rigid parts as well as rigid parts when specific assembly conditions must be met. (e.g. the flatness of sealing surfaces.)
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    A method to specify how to restrain datum features.
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    How to dimension cylindrical parts with bends (e.g tubes).


Adding new tolerancing tools in your addendum should be used sparingly. Adding new tolerancing tools can cause problems for CAD, analysis, and inspection software.

Summary and closing thoughts.

In part two, we looked at each of the five content categories of corporate addendums. Each corporate addendum is different based on their unique situation. Every addendum will not address all five of the above categories. An addendum may also include additional information not discussed in this article. 

Part three of this article will be posted next week. In part three, you will learn a few tips on creating and implementing an addendum in your organization.

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Should your company be using an addendum to the Y14.5 standard? – Part 1

About this article...

This article consists of three parts. The first part discusses whether using an addendum to the Y14.5 standard is a good practice for your company. The second part explains the five content categories typically found in an addendum. The third part provides tips on creating and implementing an addendum. 

Part 1 - Why use an addendum?

Do any of these conditions exist on your company drawings?

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    Are your coworkers confused over when to use GD&T on drawings?
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    Do your drawings contain different GD&T symbols for describing the same requirement on drawings?
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    Do your drawings use coordinate tolerances  (often called plus-mins tolerances) to locate holes?
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    Do your drawings use concentricity or total runout  symbols in places where the function of the toleranced features is assembly?
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    Do your drawings contain special tolerance requirements that are not in the Y14.5 standard but are needed to define the functional requirements of your products?

If you answered yes to any of the questions above, then you should consider creating an addendum to the Y14.5 standard.

Is creating a corporate addendum a good idea?

I can read your mind. Some of you are wondering "Why do I need to go through the expense of creating and implementing an addendum when I am getting along just fine using the Y14.5 standard alone?

However, have you considered the following?

The Y14.5 standard is like a giant toolbox with tolerancing tools for all sorts of applications.

Imagine you were in a contest and won a giant toolbox filled with hundreds of different tools. The tools could handle almost any kind of plumbing, electrical, or mechanical repair job that came along. This toolbox has so many tools that knowing how or when to use all the tools would be difficult. The giant toolbox is good because you could use the tools that you are familiar with to do many jobs. It would also be bad because there would be tools that you were not familiar with and you might end up using them in the wrong places. The Y14.5 standard is similar to the giant toolbox.

The Y14.5 standard includes tolerancing tools for many applications. Having a standard that is like a giant toolbox is useful because it provides tolerancing tools that are needed for most applications in many companies. It also can be confusing because it contains tolerancing tools that are not useful in a particular company. This toolbox approach requires users to choose from several tolerancing tools to select the one that is best suited for their application

Which tolerancing tool is best for my application?

The Y14.5 standard contains many options and over a dozen defaults. In some cases, it provides multiple ways to communicate the same requirement. The Y14.5 standard also has a few tolerancing tools that need to be explained in more detail for some applications. There are also cases where there are tolerancing tools that are needed in a particular industry but are not covered in the Y14.5 standard.

An addendum can improve the use of the Y14.5 standard and guide users in creating drawings that are clear and consistent. An addendum is of particular importance for companies working Internationally due to the variations between ASME and ISO standards.

What is an addendum?

An addendum is a document that supplements the Y14.5 standard. It may also supplement other ASME standards as well.

In some companies, an addendum exists under other names like corporate standard, engineering standard, or another name. If your addendum documents a change to a default condition or adds a tolerancing tool, not in the standard, the addendum must be referenced on each drawing for interpretation. In this case, your addendum must also be accessible to all drawing users.

The word "addendum" is a bit misleading. An addendum does not only add new tools; it can also reduce or limit the tools based on corporate need. Most addendums result in a smaller more focused standard. In fact, many addendums contain very few new tools and mostly clarify existing tools, select options, or limit the tolerancing tools in the Y14.5 standard


Although this article, for the most part, discusses an addendum to the Y14.5 standard, however it is common for addendums to encompass additional standards.

Benefits of an addendum?

An addendum can provide many internal benefits to a company as well.benefits when working with suppliers

Five benefits of using an addendum are shown below:

  1. Improve consistency  - Reducing the options from the Y14.5 standard results in more consistent drawings.
  2. Reduce confusion - An addendum can disallow GD&T symbols and modifiers that are not needed in your company. Eliminating information that is not necessary reduces the complexity of the Y14.5 standard.
  3. Reduce debates over drawing interpretation - Where the Y14.5 standard contains gaps or ambiguities, an addendum can fill the gaps, and clarify the ambiguities. An addendum can save time by; eliminating drawing misinterpretations,  and reducing debates over drawings. 
  4. Reduce costs - An addendum can encourage the use of tolerancing tools that allow more tolerance for application that do not require restrictive tolerances.. 
  5. Improve communications - An addendum improves communications with suppliers by documenting tolerancing tools not covered in the Y14.5 standard, eliminating unneeded tolerancing tools, and documenting all of the applicable standards that apply to a drawing.


Part one of this article covered several aspects of corporate addendums. It defined what is an addendum. It also discussed why you should consider using an addendum and highlighted five benefits of using an addendum.

Part two of this article will explain and provide examples of the five major content categories of an addendum. Part two will be published next week.

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Welcome to the GD&T / Dimensional Engineering Blog

The purpose of this blog is to share information on ASME GD&T and ISO GPS standards. It will also discuss real-life tolerancing issues and dimensional engineering applications, practical solutions related to the topics of engineering drawing standards, GD&T usage, inspection, gaging and measurement design analysis, and tolerance stack-ups.. This blog will become your go-to source for information on standards and all things about GD&T.

The blog will contain a variety of informative / interactive features such as: discussions, surveys, quizzes, teaching methods, tips, notices of standards meetings and publication of new standards. 

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