Many weed trimmers share a common design with nylon string fitting inside the trimmer for cutting weeds and grass. As you start the weed trimmer, the nylon string rotates fast enough to shear vegetation. Most models will release more string if you tap the trimmer on the ground while it's running, but once the string runs out you will need to refill the spool and rethread the weed trimmer to keep it operating properly.
Unplug the weed trimmer before you begin replacing the nylon string.
Remove the cover that houses the nylon string spool and remove the spool.
Check the inner area of the weed trimmer for excess grass and soil. Use a nylon bristle brush to remove the grass and soil from this area to keep your weed trimmer working properly.
Examine the spool to ensure you understand how to wind the nylon string. Look for a hole or notch to attach the end of the nylon string into. Stick the end of the nylon string into this starting point.
Notice which way the arrow points so you know which way to wind the nylon string. Begin winding the nylon string around the spool, following the arrow. Continue winding nylon string around the spool until it is full of string.
Extend the nylon string approximately 5 inches away from the spool and cut the nylon string off at this point with the scissors.
Hold the tail of the nylon string securely as you snap the spool back into place in the weed trimmer. As you are placing the spool back into position, insert the nylon string tail into the exit hole through which it must feed to cut weeds. Snap the spool into place.
Pull approximately 6 inches of nylon string out of the exit hole and replace the outer cover on the weed trimmer.
Plug the weed trimmer in and turn it on. Tap the weed trimmer onto the ground once lightly to engage the automatic feed mechanism. This will set the nylon string to the proper length for trimming.