I have experience with Ryobi and Sears weedwackers for many years. I abuse mine when edging and even weed heavily with them .090 line. What happens is that when they are forced to "dig in" to earth the resistance causes the line on the head to tighten so it cannot release. If I am cutting weeds as the manufacturer intended there is no problem until , again, excess load is transmitted into the line wound on the spool. In this case like trimming close to a chain link fence where the fence fights back , like the dirt . When I am abusing the trimmer I just expect to have to undo the hex LH nut often and loosen the line and rewind it. This can happen at frequent intervals , like every 10 minutes or ever more frequently. When properly placed back on the shaft before tightening the LH screw (not very tight) I always do "a proof of action" by pushing down the wound cartridge to see that it is free to move in and out as in "bump" action. If it is not it can be due to dirt/grass accumulation which must be removed. I also clean and place a light coating of grease on the shaft and spool (plastic), which helps. An interesting angle on the wind direction: there are arrows on my Ryobi head to show which way to wind. When it died I transferred the snap on shaft with the bump head to the Sears. It would not bump properly so on a hunch I reversed the wind direction and voila!. I guess that means the Sears engine is running backwards from the Ryobi, but have never really pursued. Again I bet this is way more than anyone wanted to hear on this subject.:laughing: