A Mild Steel Jack Nut is a type of fastener used in construction and scaffolding applications to secure threaded rods to a base plate or other structural element. The jack nut has a threaded hole in the center and a series of small teeth on the outside diameter. To install the Mild Steel Jack Nut, it is threaded onto the end of a threaded rod and then hammered into a pre-drilled hole in a base plate or other structural element.