I'm guessing the HO52 axle is the single rear wheel and HO72 is the dual rear wheel axle. Is that true?
The HO52 is the 3/4 ton axle, rated at 5200#, the HO72 is the 1 ton axle, rated at 7200#. I believe the main difference is the brake size, perhaps outer bearings on some years/models. I have seen both versions in single and dual wheel, as dual wheels were an option on 3/4 tons in some years.
