Ruff Riders Roadie Canine Vehicle Safety and Training Harness - Size Small2 Size SM2 fits dogs with a chest size from 24 to 27 inches and a maximum neck size of 21 inches Stress is placed on the chest instead of the neck of your dog The tether leash is adjustable and allows for movement Easy to use and can be left on all day in and out of the car Designed with input from a veterinary orthopedic surgeon and design engineer