I bought a stihl FS 56RC straight shaft trimmer in 2015, experimented with different types of string and I found the best was a .095 shaped string that has actually has five edges on it (grassgator commercial shaped trimmer line) I also am on my third head, I’m not buying any aftermarket stuff just stihl replacement heads, there a little over 20 bucks each, I just plum wear them out, it’s important that the head assembly that stores the string is real clean, it gets all filled up with debris and doesn’t function right, I’ve also found to pre-cut the string so that when I run out I can just take the head apart and wind the string on the 2 spools without having to measure anything, each one is approximately 15 feet long so then I cut a few 15 foot pieces wind them up 2 at a time and have them ready, it only takes a few minutes to reinstall new string for me, hope this helps
PS...Hey John, Did you forget something last Sunday? (hint...journal, I feel like a deprived little boy that didn’t get his weekly allowance... LOL)