This is on a FS70, I even got some of the heaviest stihl brand trimmer string available, and it still breaks/grinds off about as easily as the thin stuff. And then when it breaks off even with the spool head, you have to shut down the trimmer and pull the head apart to feed the line out again. Anyway, I want to get the best solution available. Does anyone use one of those heads that you clip the plastic blades onto? What about the ones you just poke new lengths of line into? I just want something that is tough and doesnt have to be taken apart to fix the line. I use this on heavy weeds clearing, edging the driveway, trimming the fence, and against broken faced landscaping bricks.