EzyDog Checkmate Dog Training Collars are Martingale collars that do not require the act of resizing for each fitting! So with all the time you just saved, you can spend it socializing and training your pup humanely and safely. The adjustable dog collar also has your pooch's comfort in mind, outfitted with a soft and durable nylon for years of use and years of comfort. Don't forget for the ultimate in dog training to pair your Checkmate collar with our amazing and innovative harnesses and leashes.