Freight class codes are the numbers associated with freight classes. There are 18 freight classes, and one must be assigned to anything shipped in the United States.
Freight classes are assigned by the National Motor Freight Traffic Association, Inc. The lower the freight class, the less expensive it is to transport the object in question. The higher the freight class, the less weight the object in question has per cubic foot. The National Motor Freight Traffic Association has a full listing of the freight class of everything that can be shipped, but general lists can be found throughout the Internet.