The bump knob holds a left hand threaded bolt that must be turned clock wise to loosen and then you wind about 6 to 8 feet of trimmer string around the bobbin. I usually put each end of the string into the 2 areas and wind them at the same time. The bobbin has arrows to show which way to wind it. Cut the line in the middle when you're finished winding. Feed the line through the holes in the bump head body and turn the left handed bolt counter clock wise to tighten. I use a pair of channel lock plumbing pliers, regular slip joint pliers don't open wide enough.
parkerdude, October 2009
