The center tie rod is sometimes also called a "drag link." The tie rod comes ready to install with permanent swiveling ends. The end pieces appear much like tie rod ends, but are quite different. Instead of a "wiggly" stud on a typical tie rod end, the ends of a drag link are merely rotating shafts. This rods job is to transfer motion from the drop arm (pitman arm) on the steering shaft to the other two conventional tie rods. The other end of the rod is connected to an "idler arm assembly" which supports it and makes steering possible. If the ends of your center tie rods have visual movement, it's time to replace the unit.