Because it is designed to trim grass and weeds in areas that are out of the reach of most lawnmowers, your weed trimmer often hits rocks, fence posts and other hard objects that eventually wear it down. When all the string is gone, it is time to restring your trimmer--a quick and inexpensive process. For Bolens-brand string trimmers, you will need .080-inch diameter replacement string, which is readily available at most hardware stores and home improvement retailers.
Disconnect the spark plug wire to make sure the Bolens string trimmer is unable to start while you are working on the unit. Place the trimmer on the ground to access the power head.
Hold the outer spool with one hand and unscrew the bump knob counterclockwise with your other hand. Remove the inner reel from the outer spool. Remove the spring from the inner reel. Using a stiff brush and a clean, damp rag, clean any debris or build-up from the power head.
Measure about 20 feet of new trimming line and loop it into two equal lengths. Insert each end through one of the two holes in the inner reel. Pull the trimmer line through the inner reel so the loop is as small and tight as possible. Wind the lines in even layers onto the reel in the direction of the arrows on the inner reel. To make sure the two lines do not overlap and tangle later while you are using the trimmer, place your index finger between the two lines to keep them apart. Insert the ends of the line into the two holding slots.
Insert the ends of the line through the eyelets in the outer spool. Place the inner reel with the spring inside the outer spool. Push the inner reel and outer spool together. While holding these two pieces together, pull the line to release it from the holding slots in the reel. About six inches of trimming line should be sticking out of both eyelets.
Hold the inner reel in place and reinstall the bump knob by turning it clockwise. Tighten it until it is secure. Reattach the spark plug wire.