Remove the mattress and box spring from the bed rails.
Locate the mounting brackets on each mattress rail.
Line the screws holes on the wrought iron headboard up with those on each rail bracket. If no screw holes exist on the headboard or they're misaligned, position the rails against each headboard leg. Use a marker to mark the rail screw hole locations on each headboard leg. Lay the headboard down on the floor, then drill a hole through each mark using a drill with a high-speed drill bit. Fasten a bolt size that matches the drill bit size through the rails and headboard legs.
Thread a washer over a 3 1/2-inch bolt. Insert the bolt into the rail screw hole and drive it through the rail hole and into the headboard hole with an adjustable wrench.
Locate the end of the inserted bolt on the other side of the headboard, and tighten a nut onto the end of the bolt with an adjustable wrench.