The Herm Sprenger Curogan Matte Neck Tech Prong collar with ClicLock quick release buckle is one of the most recognizable and popular names in obedience training tools. A safe and effective alternative to choker collars, it puts even pressure around the neck, about every half inch, pinching the skin in a band. This collar does not apply direct pressure to the trachea, so you can train your dog with little or no tugging, jerking, or pulling. The addition of a center plate connector allows the middle link to be configured symmetrically, enabling the prongs to tighten in the same direction. Made of high quality Curogan (Copper and Tin allow). Curogan is completely Nickel free, which makes it a perfect choice for dogs who are allergic to nickel. The size of this collar can be adjusted by adding or removing the links individually. Features: interlocking links, each link equipped with two blunt prongs slips over dogs head for easy on, easy off slightly beveled prong tips easy to increase or decrease in size. Additional links sold separately. Sizing instructions: collar should fit snuggly just below the dogs ears, measure the circumference of dogs neck and add 2".