Almost all U.S. LTL carriers use NMFC freight classes, although some are attempting to move to a dimensionally-based system.

Adding NMFC code to a shipment is technically optional, but the NMFC codes can help avoid reclassification and ensure you're using the correct freight class number.

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.