There is a noticeable "race width" groove in the hub. My assumption is the race spun and "self clearanced/machined" a the groove. I didn't pay much attention when trying to hit the tiny edge with a drift. They are identical (within 0.001"). The new one has to be tapped to go in, then spins once in place, in the groove. I would like to stay with the drums as that is what the car is supposed to have and they work very well for how I use the car. Yes, still small bolt pattern.