Poolmaster 12408 Replacement Filter Cartridge for Watkins 31489 Filter Equivalent to the following replacement filter cartridges; Pleatco PWK30 and Unicel C-6430 The top of the replacement filter cartridge is open 1-15/16 and the bottom is open 1-15/16 High quality spun bonded polyester material for exceptional water filtration Premium grade polyurethane and plastisol end caps