Lemme see if I remember.
Many of the late model axles have a male end that inserts into the rear differential. Some of the older models required axle stubs because the axles themselves did not have a male end. The axles were a flange type kind of similar to the front axles (but not really). For this to work, the rear differential requires a 3-4" long axle stub to which the axle will mount to.