oh, the armor plating?
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the two larger discs over his pec area on his chest are for protection from arrows and the like, but still allow him the mobility needed to strike with Mjolnir from any and all angles.
The two slightly smaller ones over his abs are to protect him from swords and daggers and such. Again, Two discs provide protection and allow for mobility.
the oftentime 3rd set of discs located below the belt USED to be armor to cover his lower abdominal area, but since his joining the Avengers and befriending one Janet Van Dyne, the two lower cirles are little zippered pouches for Thor to carry his Avengers ID card, a little glass prism, some condoms, loose change, and a pouch or two of "just add water" mead!
Funny thing about the little glass prism. I dont hink it has actually been depicted in print, but well over HALF of Thor's battles with the Hulk end before they even start. The hulk REALLY has a thing for tiny, shiny objects. He can look at them for hours.
