The Kaytee Comfort Wheel features a safe, solid running surface, quiet operation and a "tail-safe" design, allowing pets easy entrance and exit. Every Comfort Wheel comes with a heavy duty wire stand and a 2-way attachment clip, so the wheel can be used either free-standing or clipped to a wire cage. 

• Can be free standing or attach directly to any wire cage
• Encourages healthy exercise
• TIP: To keep your Comfort Wheel running quiet, place a few drops of vegetable oil on the wheel hub where the wheel spins

Small has 5.5" diameter and is best suited for dwarf hamsters and mice. 
Large has 8.5" diameter and is best suited for regular hamsters, gerbils and rats.
Giant has a 12" diameter and is best suited for large rats, chinchillas, and hedgehogs.