Source: DLA Logistic Information Service
During World War II, it was common to find different names applied to a single item of supply used by each military service. That made it difficult for the military services to locate supplies and, in most cases, impossible to share items of supply. This resulted in an item depletion situation for one service and item surplus situation for another due to different naming conventions.
To illustrate this complex issue, one only needs to consider what the name of the following item is. Is it a washer, a spacer or a shim?
The correct name for this item is WASHER, FLAT.
This is one example of why it is so important to establish a common name and description for a single item of supply. If each of the military services called this washer by a different name, there would be no way to identify and move assets from one service to another when needed. Additionally, it was determined to be essential that DOD describe all like items the same, with the same characteristics to facilitate comparison of items and avoid proliferation of like items in the DOD inventory.
Even today, commercial entities continue to justify and reinforce the need for a standardized national stock numbering system. Manufacturers, as in the case of the preceding washer, use a variety of item names for identical parts. Cataloging these items with different item names creates inconsistencies in the various logistics management systems, making it difficult to identify, separate and control inventory of items.
Manufacturers use many different commercial part numbering conventions. For example, manufacturers may refer to their items of supply using various descriptors like a Universal Product Code (UPC), a National Drug Code, and/or a Universal Standard Products and Services Classification Code (UNSPSC) as part of the item description. The NSN alleviates manufacturers from using various languages to describe items of supply by standardizing naming conventions and logistics management data.