This part is a Swimming Pool Pump Trap Lid for Hayward Pumps with O-Ring.. The model number it fits are Power-Flo LX SP1580, LX SP1700 and SP1500..
Trap Lid Diameter 6-3/8"Trap Lid...
Half Union Fitting Complete Set... The Threaded side measures about 3" Inside and the Slip Glue end measures about 1 7/8" Inside Diameter for a 1 1/2" fitting to glue inside or 2 2/3" Outside...