Turn off the trimmer and disconnect the spark plug wire or remove the battery
Remove the trimmer head cap by pressing the tabs or unscrewing it, depending on the model
Remove any remaining old line from the spool
Cut a length of replacement trimmer line to the correct diameter for your Stihl model
Fold the line in half if using a dual-line spool
Insert the line into the spool’s anchor hole or center slot
Wind the line evenly and tightly in the direction of the arrows on the spool
Leave about 4 to 6 inches of line extending from each side if required by the model
Place the spool back into the trimmer head
Thread the line ends through the eyelets in the trimmer head
Reinstall the cap securely
Pull the line ends to confirm they feed smoothly
Reconnect the spark plug wire or reinstall the battery
Test the trimmer at low speed before use