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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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