A lip, typically on the axle shaft or wheel bearing hub that the wheel is centered on to be on the same axis as the wheel bearing. This is where hub centric rings come into play to adapt the lip to the wheel bore. Some wheels are lug centric, some are hub centric.What is register.
The register is the diameter of the center of the axle (or hub center in front brakes), it fits snugly to the wheel and supports the majority of the weight (instead of the lugs) on the wheel/axle interface, and ensure that the wheel remains center true. This is known as "hub centric". Relying solely on the lug nuts/studs is known as "lug centric".What is register.
The round, raised area in the middle of the axle flange that the hole in the middle of the brake drum fits over. 4" bolt pattern Mopar axles have a smaller register.What is register.
Just to answer the question, Ford is 2.79" & Mopar is 2.81". I made a go/no-go gauge out of a piece of exhaust tubing & marked it, Ford on one end & Mopar on the other. I've simply modded the couple of Ford rims I've used in the past.Got it figured out.. The axles fit perfect. Thanks guys