My friend donated a hamster wheel for me to use, but I'm not sure about the size. It's 7.25 inches in diameter and there's about 3 inches in between the part that sticks out from the center of the wheel. It came from a Habitrail Space Station cage. If there is any doubt about it's suitability then I will just buy a new wheel, that's larger, but it would be nice to use this wheel !