⭐SIZE DETAILS: ✔ S: Φ 5.5 inches. The diameter of Nobleza small hamster ball is 5.5 inches, fit for dwarf hamsters, small pet rats, or other dwarf rodent breeds, but maybe not rats, chinchillas, and even adult hamsters. In order to ensure your rodent can enjoy a comfortable ride, please must measure your small pets accordingly before placing an order, to make sure whether the size fits your small pets. ⭐BPA-FREE MATERIAL: Nobleza dwarf hamster ball is made of high-quality & BPA-free plastic that is resistant to shattering and shocks. The transparent design with a tint of light yellow color provides proper visibility for your pets when exploring while allowing you to know about your small animal's every move and make sure it's safe. ⭐SECURITY & VENTILATION: Nobleza clear hamster ball has a safe clip-in lid, which is easy to twist and lock, preventing your pet from escaping it while running. The hamster exercise ball with ribs inside can support a better gripping power for your pet, as well as help to maintain a safe and comfortable posture, preventing the risk of injuries. The multiple holes on the surface of hamster balls provide excellent ventilation, giving enough air for your pet to breathe and work out properly.