Size M (Circumference: 8.75-9.5, Length: 2.25-3). Size L (Circumference: 9.75-11, Length: 2.5-3.25). This medium dog muzzle fits breeds such as Border Collie, Beagle, and Corgi. It is not suitable for aggressive dogs, highly anxious dogs, or flat-faced breeds like Bulldogs. Please measure your dog's snout circumference and length according to the size chart to ensure a comfortable fit where the nose does not touch the edge. Patience during muzzle training is essential to reduce escape attempts and resistance. It is normal for a dog to feel resistant and try to remove the muzzle initially. Consistent positive reinforcement with treats and praise will help your dog adjust. To reduce odor from sealed shipping, place the muzzle in a cool, well-ventilated area for a few days or wash with a mild detergent and air dry. The muzzle is non-toxic and safe for your dog. This muzzle features an innovative semi-enclosed design to help correct habits like biting, eating branches, and chewing furniture. Please