Just as a note, All of the upholstery nuts are 11mm. There is a bolt that comes loose, not a nut, on the topside, Left and right, of the rear seat back. The best way to get to tighten them up if is to A) Find an NBA player with really long arms. B) take out the rear speaker and stretch way back up in there. This would pertain to the E and X22's for sure.