Keep small critters from nesting under the dome of your large propane tank. The ProDomeSeal goes over the dome copper service line opening, eliminating the entry point for small crittersThe ProDomeSeal is designed to fit 250, 500, and 1000 gallon Propane tanks with the standard access opening size of 3″ wide and 4″ high. An easy to install, inexpensive solution to your unexpected propane tank surprises.