The AQ-4035 is an updated replacement for the AQ-4025 The AQ-4035 cartridge set fits all Aquasana countertops and all Aquasana under counter systems bought before April of 2013. The A and B replacement filters are guaranteed to be compatible with AQ-4000, AQ-4500, AQ-4501, AQ-4000W, AQ-4000P, AQ-4000B, AQ-4000N, AQ-4600, AQ-4601, AQ-4601.55, AQ-4601.56, AQ-4601.62 and AQ-4601. The AQ-4035 is our …