PREVENTING BITING: Ideal for aggressive and energetic pups, to use during training or for your everyday walks around the neighborhood. HIGH QUALITY: Made of durable, high-quality nylon that can stand up to daily use and is comfortable to wear. ADJUSTABLE: different sizes to accommodate various breeds so you can find just the perfect fit for your pup. MEASURMENT:Measure circumference of dog'mouth and dog neck.Please check the second picture and choose suitable size .If you are hesitant between the two sizes, smaller will be more suitable.Please double check before purchase. NOTICE: Please check part or video in this product listing (L-Black),which will teach you how to train dog to accept muzzle.Because dogs are anxious about wearing muzzles at the beginning: try to take off muzzles or bite through muzzles.