GIZZMO It is designed to absorb the expansion of winter freeze-up in swimming pool skimmers. The Large Skimmer Guard is 16 inches long and installs in big deep skimmers of most in-ground swimming pools. The Small Skimmer Guard is 9" Long and should be used for above ground pools. They both have 1 1/2 and 2 inch threads and features a generous bar style handle. The double threads offer convenience by accommodating most skimmers with one item.