The National Codification Bureaus or NATO Codification Bureaux (NCB) are a NATO organization that oversees the management of the National Codification System (NCS). Countries that participate in the National Codification System (NCS) follow common standards and techniques to assign National Stock Numbers (NSNs) to items of supply in their defense inventory. The National Codification Bureau (NCB) within each country centrally assigns their national NSNs. The assignment of an NSN denotes a distinctive item of supply; to eliminate confusion, the number will never be re-used.