The Herm Sprenger Black Stainless Steel Prong collar 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 German Black stainless steel, 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 dog's head for easy on, easy off slightly beveled prong tips easy to increase or decrease in size Made of high quality Black stainless steel Additional links sold separately. Sizing instructions: collar should fit snuggly just below the dog's ears, measure the circumference of dog's neck and add 3 inches. These Black Stainless steel collars with O ring come in three sizes 2.25mm gauge x 16 in overall length, 3.2mm gauge x 23 in overall length and 4mm gauge by 25 in overall length