The OllyDog Martingale Mesa Collar is the ideal training tool. This collar features an easy to use side-release buckle, aluminum D-ring, and is made with tough, washable webbing. Complete the look with our matching Urban Trail Reflective Leash. Sizing Information Small - 9"-12" Medium - 12"-16" Large - 15"-21" Additional Information When a leash is attached to the aluminum D-ring on the loop, the collar gently tightens and helps prevent dogs from backing out of their collar The martingale collar is made from very strong webbing with a variety of Colours and patterns, especially the reflective&'; range is designed to ensure pets are visible in bad weather and at night The reflective ribbon shines brightly under Street lights and in-car headlights It&';s made of washable poly webbing so you can keep your pup&';s specialty dog collar in pristine condition 2 functions of an aluminum D-ring: leash attachment Point Size Reference: Small : 9" - 12" , Medium : 12" - 16" , Large : 5" - 21"