The Boomer Ball is the perfect durable hard wearing toy. It is virtually indestructible and is ideal for those ball-obsessed toy destroyers. It can also be used as a therapeutic toy to enrich the environment of elephants, pigs, polar bears or any other bored inquisitive animal. The size selected should be larger than your dogs maximum jaw gape. Size Guide: 4 inches: Jack Russell/Westie/Yorkshire Terrier, 6 inches: Border Collie/Bulldog/Springer, 8 inches: Boxer/Pointer/Bull Terriers/Dobermann, 10 inches: Bull Mastiff/Great Dane/Rottweiler/German Shepherd.