Anchors Nylon Ribbon Collar Martingale. Martingale collars prevents neck injury that choke collars and slip collars often cause. Choke and slip collars can cause harm to a dog as they keep getting tighter when they pull resulting in trachea injury or piercing the skin. Martingale collars DO NOT do this. They fit loosely and only tighten when necessary and in a safe manner. Comes in navy blue and red. Comes in medium and large. refer to size chart for measurements.