Pump Unions Explained

What size unions will fit my pump?

Pump Unions Explained










Buttress Thread Unions:

If the pump inlet/outlet (thread tip to tip) measures 62/63mm (2.4”) across then it fits 1.5” Unions
If the pump inlet/outlet (thread tip to tip) measures 78/79mm (3.1”) across then it fits 2.0” Unions
If the pump inlet/outlet (thread tip to tip) measures 92/94mm (3.7”) across then it fits 2.5” Unions

In general a 2" Pump union is one of the more common in the marketplace.


Pump Unions Explained






Collar Size ID




Thread Type




Connection Size

2.0” (60mm)

1.5” (48mm)

1.0” (33mm)

Unions - Outside Diameters
Regarding pump unions -  2" Pump unions is one of the most common in the marketplace.
Be aware the 2" dimension does not relate to any measurement on the union.
To help in identifying your pump union the outside diameters are approximately:

1" union = 2-2/8" - 57mm
1-1/2" union = 2-13/16" - 71mm
2" union = 3-3/8" - 81mm
2-1/2" union = 4-1/4" - 105mm

Unions – Collar size and Socket (Tail piece) dimesions

Collar ID

1.5”        = 63mm
2.0”        = 79mm
2.5”        = 92mm

Socket ID

1.0”        = 33mm ID
1.5”        = 48mm ID
2.0”        = 60mm ID
50mm   = 50m ID
63mm   = 63mm ID
32mm   = 32mm ID

Pipe Sizes
The tailpiece (Socket) size can vary to fit different pipe sizes.
Eg. A tail piece with a 48mm ID will fit 1.5” pipe (1.5" is a pipe size that is referred to in the pool and spa industry that actually measures 48mm OD and has a 1.5” ID)