Question 52

The Correct Answer is A. A pipe coupling is a short length of pipe fitting used to connect two pipes or pipe sections. By definition, a standard coupling is designed to connect two pipes of the same size, end-to-end, and therefore requires **inside (female) threads on both ends** so that the male (outside) threads of the connecting pipes can screw into the fitting. ### Explanation of Incorrect Options: **B) a left-hand twist:** While specialized fittings (like certain unions or turnbuckles) may use left-hand threads for specific assembly or tensioning purposes, a standard, common pipe coupling uses standard right-hand threads and its defining characteristic is the presence of internal threads at both ends, not the direction of the twist. **C) outside threads on one end and inside threads on one end:** A fitting with an outside (male) thread on one end and an inside (female) thread on the other is typically called a **bushing** or a **street elbow/tee** (if it changes direction). A standard coupling must accept two male-threaded pipes, requiring internal threads on both sides. **D) outside threads on both ends:** A short fitting with outside (male) threads on both ends is known as a **nipple**. This fitting is used to connect two female-threaded fittings together. A coupling, conversely, is used to connect two male-threaded pipes together, requiring internal threads.