What is a pipe fitting union?

　　A pipe fitting union is a secure and semi-permanent connection between two pipes. Most pipe unions consist of two pipes connected together via a third piece. All three are threaded to make a firm connection. While pipe fitting unions are similar to couplings, they are generally easier to take apart and allow pipes of different metals to come together safely. This joining method is common in household and commercial pipe systems.

　　At first glance, a pipe fitting coupling and a pipe fitting union seem very similar. They both connect two pipes together using a male and female threading system. The main difference between the systems comes from the actual method of joining. Two coupled pipes screw together directly, one inside the other. To take the pipes apart, every pipe that connects to the coupled pipe needs to turn. In a full pipe system, this would mean the entire system needs to come apart to remove one pipe.

　　With a pipe fitting union, the two pipe ends don’t screw into one another—they each screw into a third piece. When one pipe needs to come apart from the other, the pipe fitting union piece simply screws onto one of the two pipes completely. If both ends of a pipe are attached using a pipe fitting union, the pipe may be removed on its own without unscrewing the other pipes in the system.