I'm not sure...would probably fit a 8-10 inch neck. My dog's neck is now 12in. I know it fit my neighbors shih tzu's neck when it was made to the smallest it would go. Just that he has no nose really for ihe strap to go around. As you can see in picture the collar fastens around the dogs neck & then you hook it to dogs collar & the leash gets hooked to the head collar; that way if dog manages to pull collar off his nose it is still attached to dogs regular collar.