Most Stihl trimmers use double lines. Rewinding Stihl line trimmer spools of different models requires very similar techniques. One design difference makes Stihl trimmers easier to load than many other brands. Stihl places anchoring holes on both sides of the spool chambers 180 degrees apart. Instead of cutting line to two different lengths as with other trimmers, two lines of equal length anchor at opposite sides of the spool.
Consult the instruction sheet for the machine's trimmer head to find the correct line diameter and line length. Operator manuals for the trimmers do not contain this information but details are available at Stihl's website.
Turn the trimmer off and let the machine cool. Turn the trimmer upside down to work on the cutter head. Release the autocut cover by pressing a thumb into the tab release holes on both sides of the cutter head housing and lifting the cover free. Loosen and remove the star nut on trimcut hubs to remove the head cover.
Grasp the Stihl autocut spool with one hand and press down while turning counterclockwise until the hub stops. Lift the spool free of the housing. Grasp the spool of a trimcut and simply lift the spool out, being careful not to lose the metal spring in the core of the spool.
Cut a length of trimmer line to twice the length specified for the spool. Double the line and cut it into two equal lengths. Stihl spools commonly hold two strands of line about 16 feet long.
Turn the spool over and note the arrow on the bottom that indicates winding direction. Insert the end of one strand of cutting cord into either of the anchor holes in the spool compartment nearest the outer flange. Note the two line-holding notches in the rim of the outer flange.
Wind the line in the direction of the arrow. Keep the line tight and even and wind the line in neat layers until only 5 inches remains. Place the line in a holding notch on the rim of the spool.
Anchor the second line 180 degrees from the first and again wind the line neatly in the direction of the arrow marking on the bottom of the spool. Secure the last 5 inches of the line in the second retaining notch on the rim.
Feed trimcut lines through line ports in the housing of the cutter head as the spool lowers into position. Replace autocut hubs with the lines just to one side of line ports in the autocut housing. Align the strands with the ports and snap them out of the retaining notches and into the ports.
Tighten both strands by tugging on the lines protruding from the ports. Take up all slack and the spools should snap into place on the hub. Replace covers, making sure tabs match locking ports or that the star nut is tight.