Which fitting would you use to connect two pipes in a straight line while matching their diameter?

• A. Backflow preventer
• B. Tee
• C. Elbow
• D. Coupling

Answer: (D)

Connecting two pipes in a straight line with the same diameter is a job for a coupling. A coupling is specifically designed to join two pipe ends inline, keeping the bore the same and not changing the direction of flow. It’s the standard way to extend a run when the pipes run straight and match in size, whether you’re using threaded, slip, or compression types.

The other fittings do different things: a backflow preventer stops reverse flow, an elbow redirects the line, and a tee creates a branch off the main run. If the diameters didn’t match, you’d use a reducer or a transition coupling, but for a straight, equal-diameter connection, a coupling fits best.