The Federal Stock Number (FSN) was an 11-Digit Numeric Code developed by the US Department of Defense in 1949 to identify items in the Army-Navy Catalog System. In 1974, the FSN was replaced with the National Stock Number (NSN) by simply adding two digits to the 11-Digit Code in positions 5 and 6 to signify the country of origin of the Numeric Code. In the instance of the USA, this code was 00. This enabled NATO Members to adopt the coding system while maintaining track of the NSNs created by that member.

Structure of an NSN:

The National Stock Number consists of the National Supply Class (NSC or FSC) and the National Item Identification
Number (NIIN). However the NIIN alone uniquely identifies the item, the FSC merely adds context by indicating
the general classification of the item. The format of an NSN might be described as follows:

abcd-ef-ghi-jklm

Each element, ‘a’ through ‘m’, was originally intended to be a single decimal digit. As inventories grew in complexity, element ‘g’ became alphanumeric, beginning with uppercase ‘A’ for certain newly added items. By 2000, uppercase ‘C’ was in use.

The NSN is officially recognized by the United States Government, the North Atlantic Treaty Organization (NATO) and many other Governments around the world. Government Agencies, including the US Department of Defense (DOD) and NATO, use the NSN to buy and manage billions of dollars worth of supplies annually. Currently, there are over 17 Million Active NSNs in the NSN Catalog and more than 10 Million Historical NSNs that are no longer actively used. Together, these NSNs represent more than 42 Million Manufacturer’s Part Numbers from more than 2.6 Million Suppliers.