We sell 10cm (4 inch) and 15cm (6 inch) diameter Monchballs. Monchball is designed to be bite resistant by being large enough that your dog’s teeth will just slip on the surface, rather than sink in. The 10cm (4 inch) diameter Monchball is best for french bulldogs, pugs, frugs, most cavoodles and smaller dogs. The 15cm (6 inch) diameter Monchball is for medium to large size dogs! If you are not sure, please email us a photo of your dog and let us know their breed and age, so we can make a sizing recommendation.