To answer the OP, you really can’t tell unless you just happen to know, measure the taper, call Richie, have another known rib to compare to, or happen to have seen a couple of dozen SS ribs. I started with a #1, switched to a #2, and then finally settled on a #3 adjustable rib. I couldn’t tell you the difference just by looking at a gun. There is also a #4 rib out there for a really high POI.
There are also a half a dozen or so different fixed ribs as well.