An organization known as the National Motor Freight Traffic Association (NMFTA) publishes a list of freight class designations, codes, and subclasses for many commonly shipped commodities (https://classit.nmfta.org/). You must pay a subscription fee to view this list. For more information about freight classes for free on our freight classes pages.
It might be tempting to declare that your shipment is a lower freight class than it actually is in order to secure a lower price, however, carriers will re-classify your freight for accuracy and charge you a fee for having to do so.
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.