CARNO Rodent rolling ball provide the best exercise for your pet. 18.5cm diameter allow bigger size rodent such as guinea pig to have their fun time. The transparent design also can let the owner to observe the cutiness of their pet playing. The rolling ball is ventilate, so you no need to worry your pet run out of oxygen inside the ball. The rolling ball is made by high quality materials, durable and easy to install. Screwdriver is included.