Small size: mouth circumference 4.5'', neck circumference 4.7''-10.0'', mouth height 1.8''. Medium size: mouth circumference 6.1'', neck circumference 5.5'' - 13.4'', mouth height 2.4''. Advanced silicone material,material is light and soft and elastic, no plastic smell,protect dog's comfort and health. Strap can be adjusted freely, and elastic. Wearing is very comfortable, do not make the dog feel uncomfortable. Prevent the dog bitting, prevent the dog eatting around, prevent the dog licking wounds, prevent the dog barking. Small size: mouth circumference 4.5'', neck circumference 4.7''-10.0'', mouth height 1.8''. Medium size: mouth circumference 6.1'', neck circumference 5.5'' - 13.4'', mouth height 2.4''. Large size:mouth circumference 6.5 '', neck circumference 6.7''-15.7'', mouth height 3''.