Moped Army

So I want to get a new carb for my 1967 motobecane 50v, and I'm trying to figure out what the difference is between the models on treatland.tv; Most of them say they work with motobecanes. They all kind of look the same/cost about the same, but they're labeled 13.13, 15.15, 16.16, etc. What's the difference?!!? Is one better than the other? Any insight would be greatly appreciated! I know a lot about working on cars and their parts, but I've only had my moped for a few months and I really want to fix it up! Thanks in advance!