What is the difference between airport seating of the square beams will be?

We observed a rectangular beam airport seating, first of all, what is the square bar, that is, the airport seating of the rail is a square ( Using 50 * 50 mm square tube, thickness of 3. 0毫米。 ) 。 With SJ900 SJ900m8 for example: 1, the difference to help and support. SJ - 900 for aluminum alloy, aluminum alloy stent and fasteners. SJ - 900 m8 hands as an iron, iron bracket and aluminum alloy fastener. 2, product size is completely different, On the basis of different armrest and chair foot, back support) 。