This pressure switch adapter is designed to use with Hayward H-Series and H-Series Millivolt heater models H1501, H150P1, H2001, H200P1, H2501, H250P1, H100ID1, H100IDP1 and also compatible with CZ,HM2,CPS,PSG Series models. Also fits Hayward Universal H-Series Low NOx models H150FDN, H150FDP, H200FDN, H200FDP, H250FDN, H250FDP, H300FDN, H300FDP, H350FDN, H350FDP, H400FDN, H400FDP. Weighs 4 pounds.