I don't think rats have a size called "hopper" because I don't think they hop around at that age the way mice do. Anyway, I think the equivalent age of a mouse hopper in a rat would be too big for your little one. A mouse fuzzy or mouse hopper would probably be appropriate. If you want to try rats instead, it would probably need to be a pinkie. However, from everything I've read, the movement of a mouse hopper is one of the best ways to stimulate a stubborn BP to eat.