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. Half Merchant Couplings are about half the length of Full Merchant Couplings.

Bulkhead Adapters are specially designed fittings meant to allow free flow of liquids in tank, drum drainage and other plumbing connections.