Exotic Nutrition's Treadmill Wheel is the highest quality, flying saucer-style, 100% all-metal exercise wheel on the market. SIZE: 14 inches. FEATURES: ✔ HIGH QUALITY - You'll love this wheel's silence, safety, and durability, truly built to last. ✔ PROMOTES EXERCISE - A safe, healthy way for your pet to get their exercise and stay active. ✔ VERSATILE - Ideal for Chinchillas, Male Rats, & Prairie Dogs. ✔ SAFE - Saucer-shaped wheel means there is no center axle for an animal to hit while running. ✔ HEALTHY - Flat running surface prevents curvature of the spine. ✔ SILENT - The wheel spins using ball bearing technology, ensuring it glides smooth and quiet. ✔ DURABLE - This wheel is entirely chew-proof and finished with a non-toxic powder coat for durability. MAINTENANCE: Treadmill wheels have a center bearing cartridge that is subject to wear-and-tear over time with continuous use, but a replacement will make any old wheel work like new! Some customers go years without replacing it, while others may have to replace it once or twice per year.