Female reducing pipe couplings are made to join two male threaded parts together as they feature female pipe thread on both sides. They differ from standard female couplings in that they come in alternating sizes of pipe thread so that different size fittings can be adapted to. They also feature a machined hex in the center so that a wrench can be used to tighten the fitting. They are made for use with air, natural gas, oil, and water and are made of brass for excellent resistance to corrosion.