You're only talking 10 or 15 thousandths or so, but who knows with Rhino shafts. Unless you have a break shaft and a playing shaft side by side with the ferrules out, not sure how you could tell. You are the first person on this forum I have herd of breaking one of their ferrules, then to hear you broke two of them. What are the odds in that. When you look at blank break shafts for sale to cue makers, the specs on them most all have a wall thickness greater than their playing shafts.
Good luck with your search for a good ferrule, there is a lot of people on here and the cuemakers forum that can give you a good recommendation to that if you want.