The Numbering Scheme Revolution

Finally, the time has come to change our outdated numbering scheme so I decided to share it with you. Here are some quick insights:

If you check out my post from 2019, you can see that our old document numbering scheme was designed hierarchical. The first 5 numbers were the project numbers and then there were 3 or 4 digits that were non-significant. But there was an exception for the top-level assembly and the main sub-assemblies. Basically, it looked like this: 

hierarchical numbering scheme

This numbering scheme worked very well until we became the technical office for a new customer. By then we were doing mostly engineering and technical documentation for one-of-a-kind devices. But when we started working with this new customer, the negative side of that numbering scheme began to show quickly and it got worse with each new device we designed. 

To give you just a quick insight: the new customer makes large production lines and they do between 2 and 3 per year. Each production line has around 100 devices that would be treated as a standalone project in our previous system. The problem arises because some of the devices use the same items,...”What project number should the document have and where should it be stored then?” These and similar questions all pointed to one solution:

We need a highly non-significant numbering scheme that will “allow” items to be used on different devices without misinterpretation. 

And we also need a completely new system to support it…(that was the hardest part!)

Actually, I tried this kind of numbering scheme back in 2014, because I was already aware of the cons of my hierarchical scheme. But at that time, I didn’t have PDM. This meant that I had no lock-out ability that would prohibit me from making changes to files and documents that I should not be changing. Basically, it was a very unstable system and not very nice to work with. Eventually, I got back to keeping all my documents (including fasteners) under a specific project folder with a strict policy that they can’t be used on other projects.


I started tinkering on the new system at the end of last year. I began putting all my ideas on my whiteboard (and around it) and started giving it shape. 

Somewhere in the middle it looked like this post's top image.

After approximately four months and a few miss attempts, I finally settled for a:

non-significant, easy to communicate, and ready for expansion numbering scheme that has even got a dash number:

Most probably I could have chosen a simpler version without the letter (XXXXX-DD) and never run out of numbers, but I don’t like leaving anything to chance. And most certainly I don’t want to start using an additional digit when I get to 99999-DD. 

I also know that if I order the complete standard fastener library from CAD booster, I will already use up to 30000 numbers. 

So, I decided: 

  • Standard items (like bolts or nuts or anything else that is well defined by a standard) that don’t need a drawing will start with the letter S.
  • Custom-made items and also catalog items (like gearboxes or cylinders) which all need a drawing, will start with the letter T. 

It might happen that we run out of T-numbers in the future, but in that case, I will just choose another letter (anyone I fancy) and I get another 99999 items at my disposal for the same  length.

Keeping the standard components under the letter S is barely out of convenience and I’m 99.999% sure that I will never have so many standard components that I would have to change the letter (but even if it happens, I will just pick one, no big deal).

This was a very short introduction to my new system. Let me know if there is anything you would like me to specifically address in my next blog post.

Btw. if you are wondering why I sometimes talk about documents and sometimes about items, please refer to the invaluable document written by Jörg Eisenträ’s priceless!


About the Author

Barbara Jerin

Is the creator of this blog and author of the majority of blog posts.

Comments 5

    1. Post
  1. Hi Barbara,
    Firstly, thank you for starting this blog, some really good insights into part numbering considerations.

    I am currently looking at numbering options for our company. We are planning on implementing PDM Standard in a couple of months when our new server is commissioned. We plan to use CustomTools as the number generator.

    I would really appreciate if you could elaborate a little further and maybe give some example use cases for the dash numbering. Also, is the starting letter just for “grouping/ categorising” purposes?

    1. Post

      Hi Declan,

      Thanks for reaching out! I’m glad to hear that I can help 🙂
      Yes, the dash number is something I intend to make a whole post about it, but currently I’m full in projects and with it also in testing of the new numbering scheme. I will describe fast what the dash number is about.

      In my system the dash number will be used (most probably) only for “marking” of non-interchangeable changes. For example, this means that if an item has to change because of some error in design, we usually need to create a new item under a new number to distinguish between the “old-wrong”item and the “new-correct” item.

      On the other hand, dash-numbers can be also used to “mark” parts that belong to a family. For example: you have an item that comes in various sizes, small, medium, large. So, you can have it marked like T01254-01, T01254-02, T01254-03. But I’m not intending to use it for this purpose and one of the reasons is that it’s hard to define what is a family and what not, so this could trigger questions with different answers and I’m trying to avoid this in my system. Another reason is that only two digits (99 items) might not be enough…only consider a standard fastener that comes in different sizes, lenghts…the debate of what to put under one family number can become a neverending story right?

      In the old days the dash-number was an indespensable gadget because they enabled you to put all items of one family on one drawing, but nowdays multi-part drawings can cause more harm than good.

  2. Hi Barbara,

    I have gone through the same headache too,
    The book by Frank B. Watts titled “Configuration Management for Senior Managers: Essential Product Configuration and Lifecycle Management for Manufacturing” helped me a lot.

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