The first of our martingale style collars is the Keeper Style Martingale. It uses the same tug design as the Keeper Hidden Prong collar with a sliding metal double ring that allows you to change how far the martingale can loosen. Keeper Style Martingale collars come with or without a plastic snap buckle. If you order a collar without a snap buckle, be sure that it will be able to slide over the widest part of the dog's head. All slip style (limited slip, martingale, etc.) collars should be measured the same way that you would measure for a prong collar. See the video here for how to measure.