A National Stock Number (also known as a NATO Stock Number), or NSN, is the official numerical label assigned to a standardized item of supply for the combined armed forces of the North Atlantic Treaty Organization. The National Stock Number designation is more common within the United States, specifically within the Department of Defense (DoD). There are 6.5 million active NSNs in the Federal Supply System, along with an additional nine million in the NATO system as a whole.
An NSN consists of a 13-digit numeric code in the format: 1234-56-789-0000. Each subgroup has significance.
The initial subgroup, the first four digits, is the Federal Supply Classification. The United States DoD uses these codes to group products into logical families for management and organizational purposes. For example, code 2330 refers to trailers and code 5305 refers to screws.
The remaining nine digits comprise the National (or NATO) Item Identification Number (NIIN). This code uniquely identifies items within the NATO Codification System. The first two numbers indicate the country that initially codified the item. Each country has its own specific two-digit code. For example, the U.S. is 01 and the United Kingdom is 99.
The remaining seven digits of the NIIN carry no meaning aside from identifying the specific item.