A method and apparatus for fastening structures. A first end of a body is placed into a hole on a first side of the structures. The body has an outer surface with a noncircular cross-section. A nut element is positioned on a flange at a second end of the body. A bolt is moved into a channel at the first end of the body towards the nut element on the flange on the second end of the body on the first side the structures. The bolt and the nut element are fastened to each other.