WebJunction

Important things to know:

1. All Other Services. This is basically a catch-all for industries that are in an industry group but which have no specific number for their precise activity. These are often referred to as "All Other [Name] Services" or "Other [Name] Services." Examples include 812199 for Other Personal Care Services, including hair replacement, tanning salons, etc.; 541519 for Other Computer Related Services, including custom programming, computer system integration design, and data processing facilities management services. There are MANY more examples. These are just a few to indicate that not every line of business has its own number for a very precise business and that in some cases, the number used may be a broad, catch-all number.
2. The dropping zero. If a number has a zero at the end, the NAICS system will drop the zero, resulting in a 5-digit number. When you see a NAICS number that is five digits, just add zero to get the complete number.
3. Root building. Notice how the numbers build. They start with a root. Roots are 2-digit numbers, like 61 for Educational Services, 44 for Retail Trade, and 71 for Arts, Entertainment, and Recreation, to name but a few. As additional numbers are added to the root, the number becomes more specific for the line of business within that area. The first two digits designate the economic sector, the third digit designates the subsector, the fourth digit designates the industry group, the fifth digit designates the NAICS industry, and the sixth digit designates the national industry. A complete and valid NAICS code contains six digits. Notice how added numbers indicate a more specific slice of an industry in this Example of Root building:
   

   • Root for Manufacturing: 3
   • 33 is in the area of Metal Manufacturing
   • 336 is Transportation Equipment Manufacturing
   • 3361 is Motor Vehicle Manufacturing
   • 33611 is Automobile and Light Duty Motor Vehicle Manufacturing
   • 336111 is Automobile Manufacturing while 336112 is Light Truck and Utility Vehicle Manufacturing

By the way, there's no "logical" way an SIC number relates to a NAICS number. The principle of base numbers for industry groups and roots being expanded is the same, but the actual numbers used are different. SIC coverage of the Automobile Manufacturing industry runs as follows:

37 Transportation Equipment
3711 Includes: Motor Vehicles and Passenger Car Bodies
Automobiles
Light Truck and Utility Vehicles
Heavy Duty Trucks
Kit Car and Other Passenger Car Bodies
Military Armored Vehicles

You can see how little room there is for specificity, as well as how little SIC numbers break down.

A few last important things to know:

1. Businesses can have more than one NAICS/SIC code! Think of a department store, which sells tires, shoes, and has a beauty salon, all under the same business name! This is important to know because when thinking of competitors for a business plan, it's not just the obvious competitors that could or should be included in a market study. Even though some businesses are not obvious competitors, they are competitors, nonetheless! This is also useful when the business being formed (your customer) is planning on doing more than one major activity. For instance, they may want to sell or distribute advertising specialties, but also manufacture them. They should find both numbers that apply.
2. The NAICS/SIC codes are for the PRIMARY line(s) of business. If the business does one thing primarily, and other things to a much lesser degree, they probably don't need to know those lesser numbers, unless researching those specific segments when finding articles about improving that area of their business. Therefore, if a pet grooming salon also boarded pets occasionally, only the pet grooming would apply; if they do both equally or significantly, both NAICS numbers apply (which are the same in this case). However, if the grooming salon also sold pet supplies as a significant aspect of their business, they would use 812910 for pet grooming, and 453910 for pet and pet supplies stores.
3. Learn more about NAICS by viewing the main NAICS page online. You may also wish to consult the Ask Dr. Naics FAQ that can help you understand the system or have some of your more in-depth questions answered, over and above what was intended for librarians on this module page.
4. Also view and use the 2002 NAICS Code and Titles and NAICS/SIC Correspondence Tables to see how numbers are constructed and how they break out into industries. Try selecting and following various industries to get an idea how the economy is categorized under this system.

Conclusion on NAICS and SIC