NATO Stock Number
A NATO Stock Number, or National Stock Number (NSN) as it is known in the US, is a 13-digit numeric code, identifying all the 'standardized material items of supply' as they have been recognized by all NATO countries including United States Department of Defense. Pursuant to the NATO Standardization Agreements, the NSN has come to be used in all treaty countries, where it is also known as a NATO Stock Number. However, many countries that use the NSN program are not members of NATO, e.g. Japan, Australia and New Zealand. A two-digit Material Management Aggregation Code (MMAC) suffix may also be appended, to denote asset end use but it is not considered part of the NSN. An item having an NSN is said to be "stock-listed".
The format of an NSN might be described as follows:
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 capital A for certain newly added items. By 2000, uppercase C was in use.
Federal Supply Classification Group (FSCG) 
The initial subgroup, abcd, is the Federal Supply Classification Group (FSCG) or National Supply Classification Group (NSCG). In theory, similar items would always have closely related numbers in this section of the NSN, no matter how the section is referred to. As the number of items has steadily increased and the system has become more complicated, it has not always been possible to keep similarity in numbers when the items are similar.
National Item Identification Number 
The nine digits, ef-ghi-jklm, comprise the NIIN (National Item Identification Number).
National Codification Bureau 
The ef pair is used to record which country was the first to codify the item—which one first recognized it as an important item of supply. This is generally the country of origin, meaning the country of final manufacture. The formal name of the field is CC for Country Code or NCB, because NCB also stands for National Codification Bureau. According to this system, for example, US is 00 and 01, Japan 30, Saudi Arabia is 70, the UK is 99 and Australia is 66.
The NSN is an expanded version of the older Federal Stock Number (FSN), which lacked the national-origin code labeled ef above, in the second subgroup. Items predating 1974 in warehouses are frequently stenciled with FSNs. As of 1998, the system is principally administered by the Defense Logistics Agency within the U.S. Department of Defense.
Other stock numbering systems are in use within the US DoD, but as of 2005, the NSN remained the most common and least ambiguous way to identify most standardized items of supply.
A Federal Stock Number (FSN) was an 11-digit numeric code. It was first used by the Defense Munitions Board's Cataloging Agency in 1949 to identify items in the Joint Army-Navy Catalog System. The Federal Stock Number was used officially from 1953 to 1974, when it was replaced by the National Stock Number. The conversion from FSN to NSN was typically done by adding "00" between the first set of numbers (the Federal Supply Class, or FSC) and the second set of numbers.
For example, the FSN:
Fictionalized NSNs 
It is not unheard of for certain numbers to be referred to in works of fiction as if they were NSNs—especially in military science fiction. This can be seen as a variation on the false document technique, something used creatively in order to lend an air of authenticity. For example, the M41A Pulse Rifle, from the movie Aliens, has been referred to as having NSN 3055-00-721-4790, as if it were real (though its FSG is incorrect: 30 is mechanical power transmission equipment, while 10, weapons, is probably the right FSC). The spacecraft hull repair kit that the player must use in the sci-fi computer game Mission Critical, to stop the decompression emergency, has "NSN 5920-385-19468" stenciled on the side of its plastic box.
See also 
- National Codification Bureau (NCB)
- NATO Codification System (NCS)
- Commercial and Government Entity (CAGE)
- Federal Logistics Information System (FLIS)
- List of U.S. Army weapons by supply catalog designation
- Military logistics