Configuration Management: When to Change Part Numbers and Revisions

For today’s blog post, we will be discussing the importance of when to change part numbers and revisions on manufacturing drawings. This is a major part of engineering change control and maintaining the proper documentation based on the minor and major changes made. Before we get started, it is important to mention that this blog is not meant as a “how to” of maintaining documentation and engineering change control. Many OEMs and companies maintain their document control based on their own system of rules of configuration or interchangeability (when to change part numbers, how to properly roll revisions, what letters and numbers to use, etc.).

It is agreeable that good configuration management is essential. The most important deciding factor of when to change part numbers or revisions should be based on the principles of interchangeability to your bill of materials. Sometimes companies will go off on a whim and change the part number or the revision, and not take into consideration of what that change will impact. Manufacturing drawings, parts lists, bill of materials, and drawing trees all represent how components, materials, sub-assemblies, and assemblies come together to create the end product. Therefore changing something like a part number, is a drastic change in the grand scheme of things compared to a revision change. So it is important to have rules and guidelines in place of when those important aspects of a drawing change and how to properly incorporate the change.

At VIP, we’ve seen it all. A company that we have been fabricating parts for will all of a sudden change the part number because a piece of hardware or paint color changed. This situation from a manufacturing point of view, is very cumbersome and not necessary since the actual fabrication aspect has not changed. Generally speaking, unless the part is no longer interchangeable (fit, form, and function are identical), there is no reason to change the part number. Instead, the revision should be rolled (hardware change) or a dash number added to the part number (color change) if there are multiple colors. By changing the part number, all the corresponding documentation like the drawings, sub-assemblies, assemblies, bill of materials, drawing trees, parts lists, manufacturing plans all have to be changed in order to incorporate the new part number, which is not necessary and costly since the part is still interchangeable.

Although rules for configuration changes are based on the industry and company, the rules are generally based on classes of change in relation to the influences of changes to the bill of materials. As mentioned above, the severity of the change relative to the fit, form, function, and interchangeability are classified as Class I. All Class I changes indicate a part number change because the part is no longer interchangeable if the fit, form, function are not the same, and therefore needs to be uniquely identified. Whereas Class II changes are minor changes to documentation or hardware that do not require a part number change, but rather a revision change.

If a Class I change only affects a single part at the first and only level, then only that part number would change. Whereas, in very complex bill of materials that involve intricate assemblies, Class I changes will affect not only the part with the change, but also any part numbers  of each higher level assembly that uses the changed part until the assembly becomes interchangeable. This can become a very difficult to track, manage, and maintain which is why is it so important to strictly follow the change rules. Otherwise, configuration management can easily become a disaster when the parts are manufactured.

If you have any tips on how you maintain changes in manufacturing documentation, feel free to share below. Be sure to include the industry you’re from and how you classify changes. Thank you for following along.


11 thoughts on “Configuration Management: When to Change Part Numbers and Revisions

  1. Im surprised there are no discussion responses. I will likely return to discuss at some point as this is a Major topic at my company right now and I feel like I have to create the rules from scratch. I would love to hear all sorts of advice from professionals with a good system. Ugghh

  2. We have a situation where a cast version of a part will undergo dimensional changes on the cast print (unique part number – 12345C-1) to add material on a wall. Then at the machining level (different unique part number – 12345-1) , will be machined off to get an identical part at the end, therefore it would be reverse compatible. As this is a form change on the casting drawing, I would like to identify it as a class 1 change. But others in my department feel that would be wrong as a class one should ‘always’ drive a new part number. The machined part number is what reports into the upper level assemblies. What are your thoughts?

    • Hi Brooke,

      Great question! Any physical change to a drawing requires a revision change. This forces the previous revision to be purged. So if I understand this correctly there is no physical change (i.e.: no notation at all) to the machining drawing, then there is no need to roll the revision of the machined part number. The only reason you would want to change the part number is if you would be building both from the original and the new change and want to be able to identify them separately as different parts. However, if you would only be using the casting’s change, meaning it replaces the original, and never build the original casting’s design, then just roll the revision. I hope this answers your question.


      • Thank you Britney. I agree it can be done by rev for this case. What are your thoughts on defining it as a Class 1 change, as it affects form? My co-workers feel a Class 1 is always a new part number, and I’m not sure that’s the case….?

        • Hi Brooke,

          Again, it really comes down to whether or not the change will result in the part replacing the previous design (revision change) or if the change is so major that you would be using it in conjunction with the previous design (part number change). Classifying changes simply helps to identify which of the two the change will be. If it’s a going to be a whole other part, and it does not replace the original part design, you want to change the part number.

  3. Within my company, I am idetifying areas where our QMS is lacking, and prioitizing where we need to make improvements. One such area is our ECO process. At this company, they only recently recognized the importance of having a formal ECO process, and it is relatively new and still in development. I am not the process owner, but I want to encourage them to stanadardize the method by which we determine whether to issue a new part number, roll revision, etc. I have my own opinion based on my own experiences, though some of my peers have different opinions. What I feel is best may not be necessarily the best model for this particular company, so I wanted to get your opinion.

    My belief: For a Class 1 change (form/fit/function), we should always require a new P/N, and new part numbers for any “where-used”/”reports to” sub-assembly where form, fit, or function is also changed. If form/fit/or function is not altered, thensimply roll revision of the sub-assembly.

    Our products are relatively simple, with only up to three levels in BOM structure, and a very limited quantity of parts.

    We have a partiuclar product that has a component, which is insulation cut from a roll of material. The specified width of the roll of insulation was 34″ nominal, +/- 1/2″. It should have been 34″ min, 35″ max. We have an ECO to correct the specification.

    I suppose its arguable(?) whether form fit or function changed. I say it has, as now, we can no longer accept material that is only 33.5″ wide. Hence, I want a new part number, and would also roll the revision of the where used assembly, which in this case is a finished good product. We don’t currently make use of revision control other than on prints, i.e., we do not print revision number of our finished good products on finished good assemblies (or sub-assemblies or materials). Though I aspire to hange that as well.

    If we do not change the p/n, we have no way for our incoming mterial inspectors to know when to inspect to 33.5″ min vs 34″ min.
    Nor will our material handlers have a way to identify the material in the warehouse (and to complicate matters, there is currently no FIFO used in the warehouse either).

    Are there other aspects that I am not yet considering, which might persuade me to change my thinking about my proposed Standard method (for determining when we need new P/N)?


    • Hi James,

      Revision level changes can be used in form, fit, & function changes. However, there must be revision level control in the finished goods arena in order for there to be recognition of the changes as well as any traceability. Without that, new part numbers are the only approach for segregation.

      Where the insulation change comes in, since the material must be 34” minimum, it would be advised to purge the 33.5” material anyway unless there is a use for the smaller width material. If you can use both sizes, then 2 part numbers are necessary. However, if you can only use 34” minimum width, then a purchased item like a roll of insulation should only require generating an ECO to implement the change in size. If you use a discreet drawing for the material, then a revision change would be advisable. There would be no issues with material handlers as long as the new material goes thru a receiving inspection.

      As you mentioned, there are varying opinions and methods used by different people and companies. All of them work successfully as long as there is continuity within the organization as to how the process is documented, implemented, and controlled.

      Britney Blue
      Vista Industrial Products, Inc.

  4. Hey everyone
    Does anyone know of any guidance that would tell me if an OEM is allowed to purchase parts from another vendor, then slap his part number on the item, then sell it to us for a higher price?

  5. I have worked at several major companies that used dash numbers. Mainly defense contractors. The company I am currently working at has never used dash numbers. I have been tasked to propose how this process should be used. I have not been able to find anything in writing that describes the process or how to implement it.

    I have always worked at companies that have had this process in place but not sure how to describe the use of it.

    Can anyone recommend a source that describes these Classes and how to use them?

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