Line trimmers, also known as weed whackers, are a power tools used to cut small sections of grass where lawnmowers or larger equipment cannot reach. Line trimmers use a monofilament string rotating at high speeds to cut grass; this wears down the string, reducing its length. When the string is reduced far enough it needs to be replaced. To do this, you need to understand how to string a line trimmer.
Purchase the correct type and size of string for the line trimmer. There are different size strings for different types of line trimmers; electric line trimmers use 0.065 or 0.080 inch diameter line while gas line trimmers use .080 inch up to .155 inch string. Check with the owners manual for the size string you need for your line trimmer.
Lay the line trimmer on the ground with the trimmer head facing up. Make sure the trimmer is disconnected from the power source; for electric trimmers this is the power cord, for gas trimmers this is the spark plug wire.
Unscrew the trimmer head cover. Press down on the safety tabs to unlock the cover if you have them. Turn the cover in a counter-clockwise rotation to remove the cover.
Slide out the line trimmer spool by pulling it straight up from the chamber. Open the package of string and find an end. Measure 12 inches from the end of the string and cut the line. Put the remainder of the string away. Insert the string into the notch of the spool. Pull the string an inch into the spool.
Locate the arrow on the outside of the spool, this will tell you which way to wind the string on the line trimmer. Wind the line in even rows creating layers of string until the spool is 3/4 full; do not fill the spool completely as this may cause the line trimmer to jam.
Thread the other end of the line through the eyelet on the housing. Pull 6 inches of line through the eyelet. Place the spool back into position in the housing. Align the safety tabs with the cover. Turn the cover in a clockwise rotation to screw the cover back onto the housing. Tighten the cover.
Press down on the center button while pulling the line. If the line advances at least 1 inch, you have finished; if you cannot advance the line, remove the spool, reinsert it, and try advancing the line again.