Pleatco PSR137-4 Replacement Cartridge for Sta-Rite Posi-Flo IIPTM 135, 35 TX, 35 TXR, Open with 12 Concentric Slots, 1 Cartridge Replacement filter for pool and spa cleaning systems 50% open ABS free flow cores maximize water flow through REEMAY filter media Antimicrobial end caps resist chlorine degradation and provide support to filter material for a longer life span 31-1/4-by-4-3/16-by-4-3-16 Made in the USA