Trek Dog Harness. A great harness for the daily trek! This vest harness is easy to step into and has Velcro and clip closure at the chest. Vest is waterproof and has reflective trim making it great for any type of walk you and your pup take! Our model Rosie a 17 lb. Beagle mix is wearing a size L. Don't forget the matching Trek Leash!Sizing:S: Neck: 9.5 in. | Chest: 12.9 in.M: Neck: 11 in. | Chest: 15.7 in.L: Neck: 12.6 in. | Chest: 18.5 in.XL: Neck: 14.2 in. | Chest: 21.2 in.