Bright Blue Multi Stripe - This festive unisex Multi Stripe is sure to stand out no mater what color your dog is. Adjustable Martingale Combo Collar with 2 D rings Available in 2 sizes Medium 5/8" wide = 14"-20" necks Large 1" wide = 16"-23" necks Matching 5/8" and 1" wide dog leashes are 5' long. Sizing Chart About Martingale Collars Martingale collars are designed to prevent a dog from escaping from their collar while on leash. Martingales are constructed with 2 loops. The larger loop goes around the dog's neck. The leash is then attached to the D ring on the smaller loop. When the dog attempts to pull their head out of the collar, the tension from the leash, attached to the D ring on the smaller loop, makes the larger loop tighten around the dogs neck, behind the ears to prevent them from escaping or "backing out" of the collar. Martingale collars are sometimes referred to as Training or Correction collars. On some martingale collars, the smaller second loop is actually a chain. Martingale collars should only be worn when the dog is on leash. Martingales should be removed when the leash is taken.