leonidas - Deere's prefixes are (or were) based on the general area or type machine they fit on. Generally, combine-specific parts begin with 'H' (or 'AH' if it's an assembly of some sort), cotton picker / stripper parts begin with 'N' ('AN' for assemblies), and tractor parts with 'R' ('AR' for assemblies). Sometimes you'll find a combine belt with a "n" prefixed number on it. This is a belt that was originally used on a picker, but dimensionally is the same thing needed on the combine. Pretty much hard and fast rules through about the '80's. But now there's so many different models, the part numbers are all over the place. Deere also went with the 6 numeric digits a while back to allow for more part numbers w/in the different categories ('N', 'R', 'H', etc). The numeric part of you belt part number has no correlation at all to the belt's size. These are only my opinions, based on working in a Deere parts department from '86 to '96.