Subclasses for
The National Motor Freight Traffic Association (NMFTA) created the National Motor Freight Classification (NMFC). It is used for all interstate, intrastate, and foreign commercial movement of LTL cargo. NMFC codes provide standardized freight classes to determine the transportability of the large variety of commodities that are shipped together in LTL shipments every year.
If the couch you are shipping has not been assembled yet and you are shipping various components that you can use freight class 250. If you are shipping a complete product then you should use freight class 175.
Some items, such as car transmissions, have a specific class no matter how heavy or big they are. This is called a fixed class. Items can be assigned a fixed class if the value and transportability very rarely change.