Rex Specs Ear Pro by Zeteo Tech was developed specifically to protect military working dogs from temporary and permanent hearing loss that can arise from noise exposure. Whether on a mission, at the range, on a motorcycle, or at an AC/DC concertRex Specs Ear Pro will protect your dog's ears and can limit your dogs hearing damage over time. SIZE   HEAD MEASUREMENT 2          13" - 15"     3          15" - 17.5"     4          17.5" - 21" See Rex Specs Ear Pro test Results here. Learn more about hearing loss in dogs here.