The U.S. Department of Labor lists SIC codes in an outline format that can be expanded from the two-digit level down to the four-digit level by clicking. The list appears on the Occupational Safety and Health website.
Businesses at the two-digit level are distributed among ten major divisions of activity. Examples of activities include agriculture, mining, construction, services and manufacturing. Of these, the service grouping is particularly extensive, ranging from numbers 70 through 89. In contrast, wholesale trade is divided into only two groups, durable and non-durable goods.
In 1997 the Office of Management and Budget cooperated with agencies in Canada and Mexico to develop the North American Industrial Classification system (NAIC) as a replacement for the SIC system. The NAIC system cascades to the six-digit level and is available on a U.S. Census Bureau web page. The greater detail allowed in the NAIC style of coding allows, for example, public relations agencies, outdoor advertising agencies and other specializations to be distinguished from each other within the advertising category.
A third system for classifying business activity is compiled by the United Nations and is called the International Standard Classification of all economic activities. ISIC codes are listed on the UN website.