Crystal Ball For Hamsters: Size: 4.72 InchesPets can play in the Crystal Ball For Hamsters, and the owner can observe the pet's every move. So cute This is a small hamster ball, not suitable for larger pets. Environmentally Friendly Materials: Hamster exercise balls select high-quality environmentally friendly plastic materials to protect the health of pets well. It is produced with brand-new PC material, with lock design, easy installation, convenient and fast Hollow Runner: Hollow design on both sides of the running wheel makes the running wheel more breathable and allows hamsters to aerobic exercise. There are multiple vent holes on the ball, which is safe and breathable, and your small pets can play in it for a long time Easy to Install: Adopt the lock design, it can be molded with a light press, easy to install DIY Combination Toys: This small hamster ball can be connected to external pipes, and unlimited extension, allowing you to DIY combinations to increase the difficulty of pets