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NATO Stock Number
A NATO Stock Number, or National Stock Number (NSN) as it is known among the member countries of Allied Committee 135 is a 13-digit numeric code, identifying all the 'standardized material items of supply. Pursuant to the NATO Standardization Agreements, the NSN has come to be used in all treaty countries.
Structure of NSN
The NATO Stock Number consists of the NATO Supply Class (NSC or FSC) and the National Item Identification Number (NIIN). However the NIIN alone uniquely identifies the item, the FSC merely adds context by indicating the general classification of the item. The format of an NSN might be described as follows:
Each element, a through m, was originally intended to be a single decimal digit. As inventories grew in complexity, element g became alphanumeric, beginning with capital A for certain newly added items. By 2000, uppercase C was in use.