Weedeaters are useful power tools that use fast-moving string to cut through plants. As the weedeater runs, the string wears down and new string is pulled forward to replace it. The mechanism in the spool uses centrifugal force to let out more line as needed. Eventually the spool of string inside the weedeater runs out of line. When this happens, it is time to add more line to the weedeater's spool.
Push the two tabs marked with arrows inward with your fingers and gently pull the spool up. The spool raises up to reveal the inside but will not come completely off.
Remove any leftover line from the spool.
Measure out two 10-foot lines of string. Weedeaters have two protruding strings that are spooled separately.
Feed the line through the center holes, perpendicular to each other and typically stacked so that one is slightly higher than the other. Follow the guides given inside the spool with your thread until you have 1/4 an inch of line coming out the bottom of the machine. Do not tie off or even "secure" the line at any point. By following the weedeater's spool guide the line will self-secure. Tying the line can cause damage to the spool.
Lower the spool back into position and turn the center knob on the bottom of the machine counterclockwise until you have only 6 inches sticking out of the holes. This will wind the thread onto its respective spools.