MF the lvl 3 fragments are from level 3 armor and the lvl 8 stuff is from lvl 8 armor. As marensman basically already said

But they do have the same name. I suppose that is a bit confusing.
But we listed out all the recipes in the mentor website on the elements page. You need the lvl 8 fragments for the elements for higher level runes (Absorption, Lightening or Strength). I would suppose the lvl 13 fragments have the same names too but be for the Grandeur, Superiority and Annihilation elements once they ever get popular here.
So look at them all listed in the List of Items in the game or on the mentor website to get a better idea.