11. Slide the headrest bracket into place from the top of the seatback frame, ensuring it’s positioned per the instructions, and align it with the existing holes in the seatback frame. Install the Allen-head hardware through the seatback frame and through the headrest bracket, and tighten by hand until snug. This will seat the square nut to the bracket. Finish tightening the Allen-head bolts with a 3⁄16-inch Allen-head socket.