Weed trimmers give your lawn crisp edges around sidewalks, patios, driveways and other areas around the home. The string in weed trimmers eventually will run out. One of the biggest pains with weed trimmers is knowing how to re-string the empty spool. To re-string a weed trimmer, purchase replacement string at a hardware store. There are many sizes of string, so in the absence of an owner's manual .80 mm string is a good size to place on most trimmers.
Set the weed trimmer upside down so that the string head is facing toward you. Clean all of the debris from the string head and the underside of the guard.
Remove the cap from the string head. The cap will pop off or need to be screwed off. Insert a large flathead screwdriver into the slot on the side of the head if it is a pop-off type. Twist the handle and pop the cap off of the head. If the cap screws on, turn the cap clockwise to remove it from the stringer head.
Pull the string spool out of the stringer head. For models that use a ground tapping motion to extend string, there will be a spring between the base of the head and the string spool. Be sure not to lose that spring.
Remove any residual string that may be left on the spool. If necessary, remove any melted string from the side of the spool with needle-nose pliers.
Cut a piece of replacement string 6 feet long with scissors. Insert one end into the starter hole in the side of the spool. Push the end through until it can be grasped with your fingers. Use a lighter to melt the end of the string until it forms a small ball. Allow the melted end to cool and pull the string firmly against the inside of the spool.
Wind the string in the direction the arrow marked on the spool. For most weed trimmers, the string winds counterclockwise. Keep the string as evenly spread on the spool as possible until only 6 inches remain.
Clip the 6-inch piece into the slot at the top of the spool. Return the spring to the center of the base of the head and place the spool back in the head. Place the cap on the trimmer head and thread the 6-inch piece of string through the string hole in the cap.
Secure the cap by pushing down on the cap until it locks into place or by screwing the cap onto the weed trimmer head. The cap may need to be screwed counterclockwise into the cap.