3. Your pet will not be injured or sprained if it is not open. anti-slip camber increases friction and enhances stability to avoid missteps. 2. Sturdy steel shaft and high quality PP material; thick wall and round edge. 1. Sports wheels for small pets, such as hamsters, gerbils and mice, with a maximum diameter of 21cm. 4. Silent structure, your animals can run at night without disturbing others. 5. Wide applicability, can be installed on a variety of pet cages. A fun toy helps keep your pet slim and healthy.