I've added a new options to my Etsy site, as I mentioned in a previous post: a martingale collar and a chain style martingale style.
The Martingale style collar was originally developed for the sighthounds such as the greyhound, whose necks are bigger than their heads. The collar is able to cinch up through the "control loop" and not slip over the head. Recently, it has become popular as a walking collar for all breeds of dogs, as a gentler, or soft choke collar. It should only be used as a walking collar and not left on the dog.
To fit a Martingale collar for a sighthound, measure the dog's neck right behind the ears and at the neck where the collar will rest. The measurements should fall between the listed measurements of the collar.
To fit a Martingale collar for other dogs, make sure to measure the largest part of the dog's head, since the collar has to slip over the head . Also measure the neck where the collar will sit and check to see that the collar expands and closes to fit the measurements of those areas.