A string trimmer stands as one of the basic tools that serious lawn enthusiasts rely upon to keep their yards looking well groomed from week to week. After between five and 10 hours of use, you likely will exhaust the nylon string on the trimmer's spool, and it will be time to change your trimmer line. While more than a dozen companies manufacture all shapes and sizes of gas- and electric-power trimmers, the process of changing trimmer lines does not vary much from model to model. In five minutes or less, you should be able to change your trimmer line and be back whacking weeds.
Pull the spark plug wire to prevent the trimmer from accidentally starting. Wait to change lines until your trimmer engine has cooled and the fuel tank is nearly empty. Tilt the trimmer so the spool assembly presents itself to you at chest level.
Remove the spool assembly cap, either by pressing in tabs on both sides or unscrewing a spool bolt, depending upon the model of your trimmer. Pull off the cap. Remove the spent spool, keeping the spring in place, if possible.
Pull about three inches of line from a prewound spool, which should come from the same manufacturer as your trimmer. Slide the spool onto the trimmer's crankshaft on top of the spring. Thread the three inches of line through the spool head's eyelet.
Replace the cap over the tabs until the assembly snaps in place. Tighten the bolt that holds the spool assembly in place if your model's cap is not secured by tabs.
Consult your operator's manual for the specific diameter of string that your trimmer needs. Using the incorrect size of string could overload the trimmer's engine.