Description: Durable: Hamster exercise wheel is made of high quality PC material,durable. Feature: Hamster running wheel designed specifically for hamsters and small animals, allowing them to run freely in the cage and exercise. Silent: Hamster Wheel With a silent, it will not make noise whether it is day or night, and will not disturb your rest Easy to Install: Small animals supplies is lightweight and easy to install, without complicated installation steps, just simple installation can be used. Wide Application: Suitable for various types of small pets, such as hamsters, gerbils ,mouse and other small animals Size Chart: 17cm: Diameter: 17cm/6.69in; Width: 7.5cm/2.95in 21cm: Diameter: 21cm/8.27in; Width: 8cm/3.15in Package Includes: 1xHamster Exercise Wheels or 1xHamster Exercise Wheel with Rack(Optional) Note: Please allow slightly errors due to manual measurement and different monitors.