Exotic Nutrition's new 23cm size Silent Runner wheel is recommended for small Sugar Gliders, hamsters, and mice. Size - 23cm across x 6.4cm wide track. The Silent Runner wheel is an innovative pet exercise wheel featuring a safe, solid running surface, silent roller-bearing operation and complete tail & fur safe design. Duel encased ball bearings allow for a low friction, quiet and smooth glide during use.The axle-free construction eliminates the possibility of tail entanglement, back injury or worse. No more centre axle that your pet's fur can get caught on. This design has no pinch areas, and the natural 'bean-shaped' openings allow for an easy entrance and exit, The openings will entice pets to enter and run against a preferred solid wall back. The heavy duty (pet-safe powder coated) metal stand allows for give, protecting your pet from joint pain caused by running on hard fixed surface. Running tracks are solid and have a textured interior non-slip surface for excellent grip. The interior bolt head is protected by a smooth snap-on cover. Every Silent Runner Wheel is assembled and tested in the USA.