An NAICS code is the Standard Industrial Classification number listed in the Standard Industrial Classification Manual which is published by the Office of Management and Budget. The NAICS Manual is available at your local library or on the Internet site http://www.osha.gov/oshstats. NAICS codes are used by the Federal Government to identify and classify specific categories of business activity that represent the primary line of business of a firm. SBA size standards are based on NAICS codes.