Prong Collar Rubber Tips with Plastic lock In contrast to other models Prong collars, this model is characterized in that it has a lock. This function of the collar gives it some advantages when it is inserted. Much easier. You do not have to push through it over the head of dogs, but just lock the neck. Prong Collar for pulling dogs Ideal for training of medium and large breeds with energetic and violent temper The collar is fully adjustable. Links can be added or removed as needed. To determine the proper size, measure the circumference of pet's neck and add 1' - 1 1/2'. Prong Collars should fit snug and high on the dog's neck.