National Stock Number
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A National Stock Number (NSN) is a 13-digit numeric code, identifying all standardised material items of supply in the United States Department of Defense. Under NATO Standardisation Agreements the NSN is used in all treaty countries and is known as a NATO Stock Number.
(N.B. The mapping below is unofficial and used here for illustrative purposes only!) The format of a NSN might be described as follows:
abcd-ef-ghi-jklm
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.
The initial subgroup, abcd, is the Federal Supply Class or NATO Supply Classification (NSC). Like items are theoretically grouped under like FSCs.
The ef pair is used for country of origin (final manufacture). The formal name of the field is NCB, for National Codification Bureau. The US is 00 and 01.
The nine digits, ef-ghi-jklm, comprise the NIIN (National Item Identification Number).
Originally, the ghi and jklm subgroups were envisioned to relate to one other as might the prefix and suffix of a local telephone number. All attempts to preserve this relationship had been generally abandoned by 1999.
The NSN is an expanded version of the FSN (Federal Stock Number), which lacked the NCB national-origin ef pair (second subgroup). Items predating roughly 1975 in warehouses are frequently stenciled with FSNs.
The FSN system originated in the US Department of War before or during the Second World War. As of 1998, the system was at least principally administered by the Defense Logistics Agency of the US Department of Defense.
Other stock numbering systems are in use within the US DoD, but as of 2005, the NSN remained the most common and least ambiguous way to identify most standardised items of supply.
