a fully adjustable strap ,It suits your at different of growth. Multi-Function:Prevent Dog biting, Barkingand,Chewing and other problem. Adjustable Design: The muzzles have adjustable strap and quick release buckle,making the best size for your dog light and breathable, Adjustable strap with release buckle, easy to put on colour:black Material:nylon size:S(Elastic Belt:3.9-6.8inch; Depth:1.2-2.3inch; Mouth Circle:4.8-5.6inch); M(Elastic Belt:3.9-9.4inch; Depth:1.6-3.3inch; Mouth Circle:5.2-7inch); L(Elastic Belt:3.9-9.4inch; Depth:2.4-3.9inch; Mouth Circle:6.2-8.6inch); XL(Elastic Belt:3.9-10.6inch; Depth:3.1-5.3inch; Mouth Circle:7-11inch); XXL(Elastic Belt:3.9-11inch; Depth:3.3-5.3inch; Mouth Circle:8.6-13.4inch); Front ring size: 13cm 15cm 16.5cm 18cm 19.5cm Package Contents: 5* Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.