When your pet pulls and tugs while you are walking, the collar tighten up, like a choke collar but much easier on the dog.  They tighten when a dog pulls, and relax when a dog stops pulling.  Also works to prevent dogs from backing out of their collars. Great for breeds with large necks and small heads like greyhounds.  These are great control collars for walking your dog or general training. It is not advised you leave these collars on around the house. These collars are hand made by us. We build them and stand behind them the way our Grandparents did.         Small is made from 3/4 and medium and large is made from 1 inch webbing. These collars are real adjustable I really don't make them for a very tiny dog about 20 lbs. is as small as they fit. medium for a average size Australian Shepherd or Pitt. Large for 85 lbs and up