A Martingale collar is also known as a Greyhound collar, a humane-choke, or a limited-choke collar. Martingale collars are designed for sighthounds such as the greyhound, saluki, Italian greyhound, whippet and so forth. While these dog collars are designed especially for dogs with heads smaller than their necks, Martingale collars are good for any breed. A Martingale collar has a gentle tightening that prevents your dog from backing out of his/her collar. Martingales are fully adjustable and slip over the head. Our Martingale dog collars have an extra D ring for use as a regular, non-tightening collar or as a special ring for tags. -- Because they could provide a choking hazard, It is not wise to attach tags to the regular D ring on a Martingale collar.