The square, triangle, X, whatever line is JUNK!!!!!! Think about it as soon as it hits something, it rounds over and is SMALLER than when originally put on. SO say you have a .95 line X style. The manufacturer measures it from corner to corner, the second those corners are round which is the first time you hit something thats not grass, the line is now the size of the solid interior dimensions...........MUCH MUCH smaller!
This was taught to us in Stihls Silver School! The round line is cheaper so its not a marketing ploy. They have a one hour talk on trimmer line and 2/3 of it were on this very subject.
Try out some of the black line Stihl makes. It is 135. VERY thick and strong!
Almost all other line besides Stihl (which is made in VA Beach) is made by spectra, the fishing line co. The strength differences on same diameter line is incredible. The Stihl stuff is almost 2 as strong.
Good Luck with your line problems!