SIN vs. NAICS vs. PSC: Federal Contract Classification Explained
Federal contracts use three different classification systems that often confuse new contractors: the Special Item Number (SIN) used in the GSA Schedule program, the North American Industry Classification System (NAICS) code used to define business types and size standards, and the Product and Service Code (PSC) used to categorize what the government actually purchases. Understanding how these three systems work — and when each is used — eliminates a significant source of confusion in federal contracting.
SINs: The Schedule-Specific Classification
A SIN (Special Item Number) is a GSA-specific classification that defines a category of products or services under the Multiple Award Schedule. SINs are unique to the GSA Schedule program — they don't exist outside of it. When you apply for a Schedule, you apply for specific SINs, and your contract covers only the services and products within those SINs. Federal buyers search GSA Advantage! and eBuy by SIN to find vendors capable of providing specific categories of offerings. Adding a new SIN to your contract requires a modification.
NAICS Codes: Business Classification and Size Standards
NAICS codes classify what type of business you are — not what you're selling to the government on a specific contract. They are used to determine your small business size standard, as NAICS codes are assigned to set-asides and competitive requirements. Your company may have a primary NAICS code in SAM.gov, but each contract or order you receive will have its own NAICS code based on the principal purpose of that work. NAICS codes are used across all federal procurement, not just GSA.
PSCs: What the Government Bought
Product and Service Codes (PSCs) classify what the government purchased in a given contract action. They appear in FPDS-NG (Federal Procurement Data System) and are used for reporting and analysis of federal spending. PSCs are assigned by the contracting officer when obligating funds — they may or may not exactly match the NAICS code used for competition. Researchers and contractors use PSC data in USASpending.gov to identify agencies actively spending in specific capability areas.