Subclasses for
Almost all U.S. LTL carriers use NMFC freight classes, although some are attempting to move to a dimensionally-based system.
Freight class 50 is the least expensive because it refers to the freight that is easiest to transport for the carriers.
If you don't include an NMFC code on your BOL, it is very likely that your carrier will charge you a reclassification fee and charge you the cost of shipping the freight they they determine your shipment is.