The standard of the airport chair what is the difference between the plate and other plate?

SJ - such as the airport chair 900 m1 regular seat back and SJ - standard products 900 m8 normal product back: the chair plate punching hole shape is different, different plate thickness ( SJ - Thickness of 1 900 m1. 5900 M8 thickness of 1. 8) Article, edge thickness ( SJ - Article 900 m1 edge thickness is 1. Article 3900 M8 edge thickness is 1. 5) , chair board same size, welding forming chair plate after finished the same size.