This part is a 1 1/2" Threaded X 1" Slip Heater Union with Gasket or O-Ring that matches Union.

The Union recieves a 1" pipe or fitting on one side that measures 1 1/4" Outside Diameter and then Screws to a 1 1/2" Heater Flange Split Nut on the other side. 

It will Glue to a 1" Pipe or Slice and screw to a 1 1/2" Heater Flange fitting. Don't be confused we also offer a Heater union that is 1 1/2" Thread x 1 1/2" Slip, 1 1/2" Slip X 2" to Heater or a 2" Slip X 2" Heater Union.

If your plumbing is 1" and your heater is 1 1/2" this part is correct.

This is usually found in 115V plug in Hot Tubs or 230V Hots tubs with circulation pumps.

This version is the 2nd most popular version of the 1 1/2" unions but still very rare.

1 1/2" Thread x 1 1/2" Slip is most popular.

This part is used in hot tubs to plumb to a heater flange.

Note: This listing is for a heater Union & Gasket only any other parts shown are for reference.

This is a chart for the outside of your plumbing pipes so you can figure out what size parts to order.

Note: The actual size a part is called is not the actual size of the hole in the part it is really the Inside Diameter of the pipe that would glue into that part which doesn’t make sense, since you cannot see inside the pipe. Therefore I am giving you the measurements of the outside of the pipe so you know what size part to order.  For example a part that ½” plumbing would glue in to would actually measure ¾” inside the hole of the part and on the outside of the pipe that glues into the part. 

½” Outside Diameter is ¾”

 ¾” Outside Diameter is 1”

 1” Outside Diameter is 1 ¼” 

I have never seen 1 ¼” in Hot Tubs

 1 ½” Outside Diameter is 1 ⅞”

 2” Outside Diameter is 2 ⅜”

 2 ½” Outside Diameter is 2 ⅞”