A weed eater can be one of the most frustrating lawn tools a person can use. Putting the string on once it's empty, can drive you almost insane, if you don't do it right. As easy as it looks, get it wrong and the unit holding the string will just fly off. Once you know the trick to stringing the double thread, you'll never have problems again.
Remove the unit that holds the string at the bottom of the weed eater. It usually twists right off. You may have to twist it back and forth to remove it, if it seems like it's stuck on. With a little effort, it should release.
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Cut off approximately 10 feet of weed eater string. Insert each end of string into the openings around the center of the unit that hold it. Pull the string where it fits tight around the inside section of the holding unit. Leave one side of the string approximately six inches longer than the other side of the string.
Pull your weed eater strings so they are both facing in the same direction. Insert your index finger between them, holding it against the plastic holding unit.
Place you thumb against one string and your middle finger against the other string. Lightly push down on the strings, keeping your index finger between them, and slowly wind the string in the direction that stated on the top of the unit. Usually you'll be winding in a clockwise direction.
Wind the weed eater string around the unit until your left with approximately six inches of string on both sides. Slip one piece of string through the notch on the side of the holding unit, while holding the other string in place. Once you've inserted the one string in the notch, snap the other string through the other notch on the opposite side of the holding unit.
Put each string through the holes in the side of the bottom of the weed eater where the holding unit will fit it. Once you've put the strings through the holes, twist the unit back on the bottom of the weed eater until it locks in place. Turn your weed eater on and see if the bottom unit flies off. If it remains in place, you've restrung it correctly and you can now begin working. If not, repeat all the steps above. Once the string is on correctly, the holding unit will remain attached.