This 3-part union has a 1.5" MPT thread at one end, and a 1.5" female output (inside diameter: 48 mm) at the other.
This item is used as a union for sand and diatomaceous earth filters, as well as for some heaters and pumps.
Length : 114 mm
Outer diameter (threaded part) : 1.5 inches MPT (48 mm)
Inner diameter (smooth part) : 48 mm, for 1.5" pipe