2 pak-filter replaces- PLEATCO PDM25P4 DREAM MAKER GATSBY SPA unicel 4CH-21, HOT TUB CARTRIDGE,filbur FC-0136, Handle top, 8" length, 4-5/8" diameter, bottom has 1-1/2" MPT threaded Replaces Unicel 4CH-21, Pleatco PTL18P4, Filbur FC-0121 Features 18 sq. ft.of high-quality Reemay Filtration Fabric with Expansive Flow core and antimicrobial end caps Used in pools/spas made by: Alcove, Atera, DM Industries, Dream Maker Spas, Maax Spas of AZ, Pageant Spas, Saratoga Spas, Vita Spas