Use a rod coupling nut to extend, space or level a threaded rod or stud. Coupler nuts also allow you to connect two threaded rods. Reducer coupler nuts connect threaded fasteners with different diameters, like a metric bolt and a standard rod. For high-moisture situations, choose a coupler nut with a zinc chromate finish. Grainger has a full selection of rod coupling nuts to extend, connect or anchor threaded rods.