The correct answer is B) inside threads on both ends. A pipe coupling is a fitting that is used to join two pipes together. It has internal (or female) threads on both ends, which allow it to be screwed onto the external (or male) threads of the pipe ends. This design allows the coupling to create a secure, leak-proof connection between the two pipe segments. The other answer choices are incorrect because: A) a coupling does not have external threads on both ends, C) a coupling does not have a left-hand twist, and D) a coupling has internal threads on both ends, not a mix of internal and external threads.