Environmentally Friendly Material: The Hamster Exercise Wheels are made of high quality environmentally friendly plastics to protect the health of pets. This product uses a PC material with a lock. It is easy, convenient and quick to install this product Hollow Wheel: The design of making both sides of the running wheel hollow, allows hamsters to breathe easily and do aerobic sports. There are several reliable ventilation holes in the wheel, your pet can have fun long in the wheel 'Transparent wheel': Pets can have fun in the large transparent hamster racing wheel and you can observe your pet's every move, it's interesting Simple installation: Thanks to the lock, you just need to press it lightly to assemble this product, it's easy to install DIY Combination Toys: This little hamster wheel can be connected to the other tubes, allowing you to create the other combinations to increase the difficulty of the game for your pet First, insert 4 sticks respectively. Second, line up with the notch and insert the transparent cover. Third, rotate the cover to the correct position. Finally, repeat the above steps, done.