The NATO Codification System (NCS) has been in place since the mid-1950s. It provides standards for the use of a common stock identification system throughout the NATO alliance. Countries that participate in the NCS follow common standards and techniques to assign 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 fixes the identity of each distinctive item of supply. All NSNs are uniform in composition, length, and structure.