The U.S. Department of Defense uses NSN's to uniquely and permanently identify items that it purchases. Additional Info: The NSN consists of a four-digit Federal Supply Class (FSC) code number plus a nine-digit National Item Identification Number (NIIN). For example, in NSN 1315-00-9356011: The FSC code is 1315, followed by: A two-digit National Codification Bureau (NCB) code ("00" or "01" indicates the United States), followed by: A seven-digit nonsignificant number. Collectively, the last nine digits are designated as the NIIN. The military is now permitting the use of UPC (Universal Product Code) bar codes that are found on most consumer goods. They have a database that cross-references UPC's to NSN's; See: The first link below. MSDS Relevance: Like CAS numbers, NSN's do not appear on all MSDS's. The CAS number uniquely identifies specific chemical substances whereas the NSN identifies specific products. The distinction is important because one product may contain several chemicals, each with its own CAS number. Likewise, a single chemical has only one CAS number, but will have a different NSN for each manufacturer! Inclusion of CAS numbers on an MSDS is a great idea because it is fairly easy to determine the chemical name/formula in a database. However, there are few good, freely accessible and comprehensive databases for NSN's. It is fairly difficult for a novice to locate a product's NSN or determine what a product is from the NSN. The links below are a good start. See also: CAS Number, EINECS Number, NAICS, UN/NA Number