Martingale collar. Adjustable from 30.5-40cm (12-16″). The collar is 5cm (2″) wide.
Martingale collars are also known as humane choke collars. They provide more control without the choking effect. They are originally made for Sighthounds because their necks are larger than their heads and they can often slip out of regular buckle collars.
Martingales are often used for Whippets, Greyhounds, Galgos and other Sighthounds.