Provide stimulating exercise for your small animal while they roam securely. With this exercise ball your pet will get more movement which will improve its health. The vented design keeps air flow during activity. Sizes: 12.7cm (5") : recommended size for tiny critters such as robo hamsters and dwarf hamsters, or mice. 17.5cm (7") : recommended size for small critters such as mice, smaller hamsters and gerbils. Exercise balls can be beneficial and fun. The key is to use it SAFELY: Supervise pets at all times. Ensure you are using the correct size ball for your species. Ensure that your pet is ready for exercise and comfortable. Clean before & after each use. Make sure the ball is closed securely before use and has the proper ventilation slots. Avoid the sun, use only indoors in cool areas away from hazards such as other pets. Limit roll time, start with a few minutes per session and add on gradually.