If you are unable to determine an appropriate code for an industry, pick a company in that industry and search for that company in a database, Such as Mergent Online, and see what codes are assigned to that company.
Data Axle – This business phonebook from across the U.S. can also show key employees and some financial information. It is very good for data on small private companies. It is the only way to find information on the various locations of a company. Two great features are the ability to modify a search along geographic lines and a Custom Search that can be used to develop a detailed, customized directory. Data can be downloaded into Excel.