The Department of Defense used Federal Stock Numbers from 1955 to 1974 to catalog items commonly used by the department. The Federal Stock Number was replaced by the National Stock Number (NSN) in September 1974. The NSN is used to catalog items throughout the federal supply system, according to the Defense Logistics Information Service.
There are millions of NSNs in the system, which is recognized by the United States government, NATO and other governments around the world. An NSN is a 13-digit code, according to the Defense Logistics Information Service. The first four numbers identify the Federal Supply Class. The next two digits identify the country of origin. The last seven digits, formatted 111-1111, form a unique number.