I have tried straight shaft trimmers, but I could never get used to the counter clockwise rotation. I am right handed, and the curved shaft trimmers that rotate clockwise just make life easier. Admitted, I enjoyed the extra power available in those rare instances it was needed in the harness up-straight shafts, but was always willing to take a bit more time with the bent shaft to wade thru tall stuff when the occassion presented itself. It seems, that trimmers, and threads keep wanting to put on heavier and heavier line, but one day, I used the 18 Volt rechargable Black and Decker trimmer that I bought my wife, (she can't start a gas trimmer - just can't pull fast enough on the rope) - it had .065 line in it, and has auto advance (no tap), and I was amazed at how fast and efficient it cut tall or short stuff. The next logical step was to see if this light string would work on the bent shaft (JD 105C). First of all, I got the professional grade, I found that I could wrap about 2 times as much string on the spool, Here is what happened. 1. Cuts way faster with less fraying than the heavier line. 2. Fuel lasts longer 3. The only concern I had was would there be enough momentum for the string to advance when tapped, and that turned out to be no problem. I will never go back to thick diameter string - It is like mowing with a dull blade on the mower - Takes way to much power.