The National Motor Freight Traffic Association (NMFTA) publishes a list of freight class designations, codes, and subclasses for commonly shipped items (https://classit.nmfta.org/). A subscription fee is required to access this list. You can learn more about freight classes from the experts at Koho for free on our freight classes pages.
The class determines the cost of the shipping. The lower the class, the lower the cost.
Yes. If your shipment can be stacked, it allows the carrier to fit more freight into their truck.