Please check the 7th image in the left side of the product web page and product description part,which will teach you how to train dog to accecpt muzzle.Beacuse dogs are anxious about wearing muzzles at the beginning:try to take off muzzles or bite through muzzles.NOTICE: Place your forefinger under the tape muasure to ensure enough space for your dog to be comfortable.Your dog must be able to pant and have free tongue movement. Notice: Not suitable for pitbull mix and all other dogs with a shorter snout.MEASURMENT:Measure circumference of dog'mouth and dog neck.Please check the size map and choose suiable size .Please double check before purchase.HIGH QUALITY: Made of durable, high-quality nylon that can stand up to daily use and is comfortable to wear.XX-Large Size - Snout strap 11-15 in, Neck strap 9-22 in.Suitable for normal size Great Dane,rottweiler,Mastiff and so on.