Surface of aluminum cone rings: the conical area is always smooth and non-serrated. The back side now has either 18 milled grooves for gear housings with milled grooves (all standard-versions), or has a knurled / serrated surface for knurled / serrated gear housings (most reha-versions).

Photo above: aluminum cone ring with milled grooves on the back side for housing with milled grooves

Photo below: aluminum cone ring with smooth surface for knurled housing