Which characteristic allows a pipe coupling to connect pieces of pipe?

A pipe coupling is designed to connect two pieces of pipe, allowing for the continuation of flow through the system. The characteristic that enables this functionality is the presence of inside threads on both ends of the coupling. These threads engage with the external threads on the ends of the pipes being connected, creating a secure and tight connection.

Inside threads provide a method for mechanical joining that not only ensures the pipes remain connected but also helps in maintaining the integrity of the pipeline under pressure. This is particularly important in systems where fluid flow is critical and leaks must be minimized.

While other options may represent different types of fittings or couplings, they do not facilitate the same level of secure connection for straight pipe runs as a coupling with threads on both ends. This design is widely utilized in various piping systems for its effectiveness in joining pipes of the same diameter and ensuring system reliability.