Every snail will be at least 3 mm in length.  If you need larger snails, see my ramshorn lots. This species has a very fragile shell, making it a popular feeder snail.  Also an interesting tank inhabitant, see behavior "spinning".  Equally happy in cold water tanks and in tropical tanks, they can survive water in the high 80's  to the brink of freezing.  Their radula (tongue scraper that they use to eat algae, periphyton and dead plants) is literally too fragile to damage live plants.  Short lived, reproduce freely in environments without predators (I had guppies that learned how to poke a hole in their shells and pull them out. If you have inquisitive and hungry fish you may never see babies or even eggs)