The Underground Fence Collars are compatible with DogWatch, Invisible Fence Brand, and PetSafe receivers. LupinePet Underground Fence Collars have two heat-sealed holes, a hole spacing of 1.25 inches and hole diameter of 3/8 inches. These collars do not have a D-ring and are not intended for leash-walking. Lupine Pet partnered with YKK, the leading buckle manufacturer, to design the optimum quality, strongest plastic buckle on the market. Designed specifically with dogs in mind and featuring an easy, convenient side release. Collar is 3/4 inch wide and expands from 16 - 24 inches Convenient and strong buckle Made with durable, lasting webbing Heat sealed holes for your receiver