Really Right Stuff ball heads now utilize our patented R-Mount interface for mating the clamp to the ball head's stem in the most secure manner possible. The R-Mount's rosette will prevent twisting at the coupling point between the two pieces of hardware over time, and will assist in eliminating "play" that results from regular use on the earlier tongue-and-groove designs. Users who wish to use an SC-ARC Clamp clamp with a rosette ball head will require an SCA. The adapter is a simple interface which will be installed (via the supplied mounting screw) between the ball-stem and the clamp, with the R-Mount rosette facing downward, and the Arms-17s standard spacing facing upward. Really Right Stuff Hardware and SCA Adapter RRS-9000079