The FitBark 2 and FitBark GPS will work with most collars up to 1.5” (38.1 mm) wide.Related ArticlesCan I use FitBark devices on a harness?What collars are compatible with the FitBark device?I’m a new user. How do I setup a new FitBark device?My FitBark device is damaged or got chewed on. Now what?What collars are compatible with the original FitBark (2015)?