He's not talking about regular ramshorns. The mini ones (which I also got an infestation of from plants from a major online seller) don't ever get bigger than a few mm. They're just a fricken mess. Assassin snails were the only thing that worked for me. Havenít seen a mini in almost a year (plenty of regular ramshorns and pond snails though!).
Betta Maniac is right. These little mini ramshorn snails are pretty freakin' tiny. Like 1 mm in diameter. Hard to pick out of the tank because they're so stinkin' tiny. A total nuisance much more so than regular sized ramhorn snails, because at such a tiny size, these guys are already breeding.
Wait, so you're telling me that an assassin snail that's like 20 times bigger can still get into the shell of a tiny ramhorn snail? I originally thought of going the assassin snail route, but scrapped that idea because I thought there's no way an assassin snail is gonna be able to get into an tiny ramshorn snail's shell.