Our BioThane Sport Collars are made with an "O" Ring in the center to offer a quick, easily accessible place to clip your leash. These are great for the avid outdoors person or an everyday collar. BioThane is made in the US and is waterproof, durable, scent proof and easy to clean! If there is a size you're looking for that we don't have listed please reach out to us. Custom orders are our specialty! Questions on sizing? Sizing is to the middle hole with 2" on either side. For the BioThane Sport Collars , please measure at line #3 on the dog silhouette. For more info visit our sizing page!