Pro trainer slip collars are training aids only and are to be used under supervision at all times. These slip collars are built upon our standard command slip collar alternatives to traditional choke chains but with a few different features from requests from trainers over the years. We switched to smaller rings and added a leather stopper tab to help get a secure "fitted" collar feeling when in use.   sizes: 3/8″ x 16″, 18″, 20″, 22″, 24″ and 26″ Sizing is measured from the inside of one ring to the other ring. Please be aware that the leather tab decreases the overall opening length by 3 inches.