Originally Posted by
79pmooney
I've been riding 13 tooth freewheels since the days of dinosaurs. (Well, 1973 but they were well established earlier.) 7-speed 12 tooth FWs since 1995 and I was a latecomer there. The SunRace website shows both 13t and 12t FWs now.
If I had to guess, 12t cogs went along with the introduction of 7 speed, and 13t might have been the limit with 6 speed due to the way freewheels are assembled. But just because I haven't been able to find a 12t 6 speed freewheel doesn't mean it didn't happen.