Here is a chart for RTJ ring groove facings. It’s very specific to my own use case but maybe somebody else will find it useful. I guarantee nothing, if you use it, it’s at your own risk. Bottom width is the size at the bottom of the groove, Largest Ball is the largest ball that will sit tangent at the top of the groove, and well, Smallest is the one that will sit on the bottom and touch the two sides. Obviously you want to be somewhere between, not at, theses sizes. Also, the lists on the bottom denote the Depth, Width sets and the numbers that follow are the R sizes that match that set.