Replacing trimmer line is safer and easier when the engine or battery is completely disconnected and the correct diameter is used. A neat winding pattern prevents jams and uneven feeding.
Make the tool safe
For a gas trimmer, switch it off and disconnect the spark-plug wire; for a battery model, remove the battery. Wear eye protection and gloves. Clear grass from the guard and photograph the spool orientation before opening it.
Match the line
Read the manual or spool marking for line diameter and length. Line that is too thick can overload the head, while line that is too thin breaks quickly. Use line intended for the trimmer and keep the loose coil away from children and pets.
Wind evenly
Thread the line through the anchor hole and wind it in the arrow direction, keeping each turn beside the previous one. Do not cross or overfill the spool. Leave the specified tail length and hold it in the retaining notch while reinstalling the spool.
Test the feed
Secure the cover and pull the line gently to confirm it releases. Reinstall the guard and battery or spark-plug connection, then test at low speed in an open area. Stop if the head wobbles, the line strikes the guard, or the feed does not work correctly.
Clean the head after mowing and replace brittle line before it becomes a mid-job failure.