It takes 5/8 inch marbles.
The reason I like this pump design is because it doesn't let the marbles clack together when there are no marbles in the feeder. It is also less likely to jam then a previous model I built.
Added a picture of the pump installed in the dragon marble reservoir.
The marbles enter through a hole between the feet and tail and exit through the mouth.
The dragon was already made, so I had to fit the new pump underneath as best I could.