Companies often describe the competitive environment and list their top competitors in their 10-K report to the SEC. Read "Item 1. Business" or search the text of the report for the words competition or competitor.
You can find the 10-K report on the Investor Relations page of the company's website or at the SEC's EDGAR database.
NAICS (pronounced "nakes", rhymes with "snakes") codes are used by the government and publishers to organize and present industry data.
NAICS codes classify establishments based on similar processes or means of production. Codes use a two to six digit level of detail, from broad sectors like manufacturing and retail (2-digit codes) to individual industries (6-digit codes).
31 - Industry Sector - Manufacturing
311- Industry Sub-sector – Food Mfg
3111- Industry Group – Animal Food Mfg
311111- Industry –Dog & Cat Food Mfg
Many databases offer profiles of public companies that include lists of the company's top competitors. This is a fast and easy way to find similar companies.