A cow magnet is a veterinary medical device for the treatment or prevention of hardware disease in cattle. Traditionally, cow magnets were strong Alnico magnets about 1 cm by 8 cm (0.4 by 3.1 inches) in the shape of a smoothed rod, but today they are more commonly several ring-shaped ferrite magnets attached to a stainless-steel or plastic core, in the same shape as the single-piece original. Newer designs to help increase effectiveness include a cage design, in which the magnet holds metal objects inside a protective plastic framework. Even newer designs include a stronger array of rare-earth magnets inside a stainless steel body that resembles the original Alnico design.