Pump union, with o-ring, for 1.5-inch pipe.  This union works with several brands of pump, notably Waterway and ITT/HydroAir.  The thread is of the asymmetric "buttress" type (also known by the initials MBT and FBT for the male and female versions respectively).

Dimensions
Internal diameter of the thread : 75 mm
External diameter of the corresponding male thread on the pump : 78 mm
Connect to 1.5" pipe (external diameter: 48.3 mm)

Références
Waterway : 400-9230