How Do You Tell What Flex Your Irons Are?

How Do You Tell What Flex Your Irons Are? “L” denotes “ladies flex” “A” or “M” denotes “senior flex” (might also be designated “AM” or “A/M,” or “Senior”) “R” denotes “regular flex” “S” denotes “stiff flex” (might also be designated “Firm”) How do you tell if your irons are stiff or regular? What’s the difference