A merchant coupling is a fitting used to join pipes, of similar size, together in a straight-line run. Merchant steel fittings are designed with Dryseal Taper Threads (NPTF) for more critical applications. NPTF Dryseal threads produce a mechanical seal by the mating and slight crushing of the threads when a wrench is applied to tighten the fittings.

Hex nipples come in handy during applications that require you to connect two brass or steel pipes, both with female ends. Common applications involve automotive, plumbing, or industrial.