I am working on the 3" mark, I can get the Hoss in with a bunch of warm up but it takes about an hour or more all in. Limit? I am sure there is but I have no idea what it would be, probably depend on anatomy for one thing. I don't think I can get much bigger than 3", my hip/leg bones get in the way with the Hoss unless I am positioned just right. I have seen two litter bottles inside a anus so I know the anus can stretch quite a ways.