The Echo SRM 210 Weed Trimmer is one of the most versatile and available trimmers on the market. It can be found at most "big-box" home centers as well and lawn and garden stores. Parts and accessories for this tool are easy to obtain and are relatively inexpensive. You can do most of the minor maintenance on the SRM 210 yourself, including including restringing the machine.
Move the start/stop switch to the stop position and disconnect the spark plug wire to ensure that the engine will not start while restraining the weed trimmer.
Remove the spool from the drum by turning clockwise and lifting it out once it is free of the inner drum.
Insert a 20-foot piece of trimmer line through the molded loop on the bottom of the spool. Adjust the line so that one end is six inches longer than the other. Wind the trimmer line onto the spool clockwise with the inside spool facing you. Hold the lines with your index finger to make sure they stay tight and close to the hub. Wind the lines until there is approximately eight inches of trimmer line remaining. Place the 8-inch pieces through the notches in the spool.
Feed the ends of the trimmer line pieces through the islets in the trimmer housing.
Align the pins on the inner drive with the slots in the spool and push the spool onto the inner drive until it engages. Pull both of the trimmer strings to disengage them from the grooves in the spool. Turn the spool counterclockwise until it stops.
Reattach the spark plug wire, slide the run/stop switch to the run position, start the engine and tap the spool on a hard surface to ensure that the string has been installed correctly and does not bind in the trimmer.