The main difference between the 72 and 52 axles was the 7200lb third member had a load bolt to prevent ring gear deflection with heavier loads as well as double taper roller bearings on the pinion shaft. The 5200lb third members don't have the load bolt and used a double ball roller bearing. The actual axles and wheel bearings were the same between the two. As far as interchangeability the two can be swapped with each other as well as the pinion, carrier and ring gear. The H052 was a 3/4 ton axle while the H072 was used by both 3/4 and 1 ton trucks, suburbans, and delivery vans.