You are buying on a 2" Slip which measures about 2 3/8" ID X 2" which measures about 3" OD Heater Union with Gasket. The Union receives a 2" pipe or fitting on one side that measures about 2 3/8" Outside Diameter and then Screws to a 2" Heater Flange Split Nut on the other side that measures about 3" on the outside of the Threads. It will Glue to a 2" Pipe or Slice and screw to a 2" Heater Flange fitting. Don't be confused we also offer a Heater union that is 1 1/2" Slip X 1 1/2" to Heater or a 1 1/2" Slip X 2" Heater Union. If your plumbing is 2" and your heater is 2" this part is correct.
This version is the most popular version. 1 1/2 x 1 1/2 is 2nd most popular and 1 1/2" X 2 is 3rd most popular.
This part is used in hot tubs to plumb to a heater flange.
