Stihl makes a wide variety of weed whackers. Many Stihl trimmers come with different cutting heads to accommodate different types of trimming needs. Just like any other string trimmer, it is necessary to take apart a Stihl weed whacker head when the string runs out. Removing the head is a bit different than many trimmers because there is not a bump knob to remove. The trimmer shaft also requires locking in order to take apart the head from the trimmer.
Shut off the Stihl trimmer and allow the head to come to a complete stop. Disconnect the black spark plug wire boot from the top of the spark plug. Place the Stihl trimmer on its side with the fuel tank fill cap pointing up.
Find the small hole on the shaft of the trimmer just above the trimmer head. Some Stihl trimmers have the hole above the trimmer head.
Insert the round stop pin tool that comes with the trimmer into the hole. If you cannot find the stop pin tool, insert a 16-penny nail into the hole. Rotate the head until the inner hole allows you to push the stop pin or nail inward to lock the shaft.
Turn the nut on the bottom of the trimmer head counterclockwise with a wrench. Remove the nut and pull the trimmer head straight off the shaft.
Twist the inner spool counterclockwise with your hand while holding the outer spool firmly in your free hand. The head is now disassembled and ready for restringing.