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    When the FMS customer asks for a particular part number and we cross that number to an NSN through FEDLOG or some other tool and then provide them a different part number than what is in their publication but is assigned to the same NSN what process ensures the same form, fit, function, (suitable substitute role) for that part? Direct question from customer. "Can you please confirm that when we request an alternate part number/ cage code approval that there is a whole engineering process that occurs to approve it."


    It is often the case that a given National Stock Number (NSN) may cross to multiple part numbers, for example when DoD procures comparable, like items from more than one vendor.  Your question has to do with the process intended to ensure that part numbers noted in our logistics information systems as ‘suitable substitutes’ actually are interchangeable in terms of form, fit and function, and this is a primary responsibility of the Defense Logistics Agency (DLA), the organization largely responsible for ‘stocking the shelves’ for DoD. 

    Assigning part numbers or NSNs, including identification and characterization of the material and linking of the various part numbers and NSNS as appropriate is the DLA function known as ‘cataloging’, and the system is called the Federal Logistics Information System (FLIS). Note that DLA will tend to use the term ‘reference number’ rather than ‘part number’, a reference number being the part number paired with the associated Commercial and Government Entity (Cage) code, which identifies the manufacturer of the component. No reference numbers will be linked in DoD logistics information systems, e.g., WEBFLIS or FEDLOG, etc., without undergoing the cataloging process, a part of which is the engineering and other research required to ensure that different but linked part numbers or reference numbers in fact are proper substitutes. The bottom line is that using the appropriate documentation for your system, for example a bill of materials or an illustrated parts breakdown, will provide government or commercial part numbers/reference numbers. Accessing those numbers in WEBFLIS will reliably identify applicable NSN’s and alternate part numbers.  For more information, the process is described in detail in the Federal Logistics Information System (FLIS) Procedural Manuals Volumes 1-13, which may be accessed at

    For example, the International Cataloging Policy discussed in Vol 1 describes essentially the same process for international or FMS customers. That overall document, sometimes called the ‘bible’ of cataloging, includes detail in Vol 10 on any and all DLA/Service cataloging codes you may encounter.  For more help, including tutorials, or if you should encounter incorrect information, DLA assistance and feedback can be effected easily via their website at

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