On some applications the plane might require a "fixed" non moveable linkage point. In order to do this they want you to solder the clevis on so it can not move in or out and locks the control surface in place. On the other hand what you described with the clevis that has internal threads that screws onto a rod that has threads on it, is another type of linkage that allows you to adjust the position of your control surface. You can twist the clevis in or out which will make your control surface move up or down.