Male hex nipples are made to joint two female threaded parts together as they feature male pipe thread on both sides. Reducing hex nipples are made to be used when alternate thread sizes on either end are needed. They also feature a machined hex in the center so that a wrench can be used to tighten the fitting. Made for use with air, water and oil. Steel fittings provide superior strength but are liable to corrode. The zinc plating provides marginal corrosion resistance.