A government NSN, or National Stock Number, is a way of identifying items within the National Supply System. It consists of 13 digits, the first four of which point to the item's Federal Supply Class, and the rest stand for a particular item.
NSNs are used by the General Services Administration (GSA), the Department of Defense (DoD), the Postal Service and other governmental bodies which need to requisition weapons, tools, office supplies and other items needed for day-to-day operation of these structures. GSA runs the GSA Global Supply federal program, which provides about 400,000 everyday items such as computers and office supplies to federal customers. Out of these products, 80,000 have NSNs.
NSNs can identify spare parts of a particular product as well as a whole item. These numbers are assigned by a governmental entity that requisitions the items, not by the producer. Federal Supply Class (FSC) is designated to a group of products and constitutes the first four digits of the NSNs. For instance, an NSN for a particular tool would start with the numbers 5110. A "bolt" has an identifier 5306, and an NSN for any pen would start with a FSC of 7510, which stands for office supplies. GSA does not assign NSNs for every item and uses prefixes for short-lived products, such as TL1 for tools and OS3 for office supplies.