TerreMax part D3412P: Adapter: 3/4" Male x 1/2" HOSE BARB Hose Barb. As the maker lists it: 3/4" 1/2" size, polypropylene. Taken from the TerreMax 2026 price sheet (xls) + 2026 catalog, page 62.
The same part number is listed in the Green Leaf 2026 catalog, page 39 (TerreMax is Green Leaf Inc.'s brand).
Not sure this is the right part for your tank? Call 866-418-1777 with the tank model and the fitting size and we will check it against the maker's specifications.
