Guardian Gear – Dog Puppy Martingale Chain Collar – 6 Colors – S, M, L Our Guardian Gear, Martingale Dog Collars combine the convenience of an adjustable collar with added safety and control of a choke-style collar.Collar size adjusts as pressure is applied to the leashLimited closure guarantees that the collar will not injure pets Material: 100% Nylon; Metal chain link To determine the proper size, measure the circumference of pet neck and add 2″5/8 wide (small) Fits necks 13″-18″3/4″ wide (medium) Fits necks 16″-24″1″ wide (large) Fits necks 22″-34″