The metal OASIS® SHIELD-GUARD® protects pets' valuable water supply by providing a sturdy metal shield between the water bottle and the cage wires. It prevents animals and birds from having access to the bottle and cap, and eliminates chewing the water bottle through the cage wires. Simply place a Shield-Guard between the cage and the water bottle and bend the tabs down to attach. Suitable for use with small animals (such as hamsters, gerbils, hedgehogs, rats, mice, guinea pigs, chinchillas, ferrets and rabbits), and many kinds of birds and reptiles. Fits 4 & 8 oz. Water Bottles