Size 4 is recommended for the following breeds: mastiff, clumber spaniel, giant schnauzer, Great Dane, Newfoundland, ridgeback, rottweiler, and similarly sized dogs.
The Sizes go from size Zero thru size Five, so Size 4 is one size under the largest size. For example, Size 3 is recommended for the following breeds: Afghan, airedale, boxer, briard, chow chow, dalmatian, doberman, greyhound, German shepherd, husky, Labrador, pointers, retrievers, setters, springers, Weimaran, and similarly sized dogs, while Size 5 is recommended for the following breeds: bloodhound, large danes, mastiffs, St. Bernard, and similarly sized dogs.
A little more info: The patented Halti headcollar, designed by Dr. Roger Mugford, gives you total control when walking your dog. Calms boisterous dogs. Simplifies training. Restrains biters. Reduces fears. Reforms fighters. Assists with restraining dog during veterinarian or grooming visits. Calms hysterical car travelers. Halti stops pulling because if you guide a dog's head, the body will surely follow.
Awesome! Is he a pretty large Shepherd? Those are such great dogs. I used to keep dogs in my home instead of being dropped at kennels by their parents. Shepherds were always a favorite! I realized I had a gift for dog-speak lolol. I've even thought of writing a book haha