An organization named the National Motor Freight Traffic Association (NMFTA) publishes a list of freight class designations, codes, and subclasses for frequently shipped commodities (https://classit.nmfta.org/). You must pay a subscription fee to view it. Find more information about freight classes from the experts at Koho for free on our freight classes pages.
Freight classification groups products based on similar density, stowability, handling and liability so carriers and shippers have an effective way of communicating the ease of transporting said freight.
NOI stands for Not Otherwise Indicated. This is used when a commodity does not have an NMFC code. In these cases, density is usually used to determine freight class.