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.
No. If you claim that your freight is a lower class than it actually is, your carrier will likely find out. They will charge you a fee for reclassifying the freight and charge you the appropriate amount for the actual class of your freight after it has been shipped.
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.