What is the difference between 4,6,8 digit SIC codes?

Standard Industrial Classification (SIC) codes are four digit numerical codes assigned by the U.S. government to business establishments to identify the primary line of business of the establishment. The classification was developed to facilitate the collection, presentation and analysis of data; and to promote uniformity and comparability in the presentation of statistical data collected by various agencies of the federal government, state agencies and private organizations. The classification covers all economic activities.

6,7,8 Digit SIC Codes

U.S. SIC codes are defined at the 4-digit level. If you see a SIC code that has 6,7, or even 8-digits, it is not an official U.S. government SIC code. These 6,7, and 8-digit codes have been created by private data companies to help further classify industries for marketing and identification purposes. SICCODE.com uses the 4-digit SIC codes and includes mapping to the 6-digit NAICS codes.