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.
NMFC stand for National Motor Freight Classification. This is a classification system used for interstate, intrastate, and foreign commerce movement of LTL shipments. You can learn more on our freight classes pages.