Trimmer line is the fast-spinning nylon filament that does the actual cutting on a string trimmer. It wears down as you work, so understanding how to choose, load and maintain it helps you get clean cuts and avoid downtime. The details vary by model, but the principles are consistent: use the line diameter and type the manufacturer specifies, keep the head fed correctly and always operate with the guard in place.
How a string trimmer cuts
A string trimmer spins a length of flexible line at high speed. The tip of the line slices through grass and light weeds. As the line hits hard surfaces it frays and shortens. According to the operator manual for the Greenworks 24V 12-inch trimmer, the machine is equipped with a line cut-off blade on the guard that continuously trims the line to keep a consistent cut diameter. The manual also explains that you should advance the line whenever the motor sounds faster than normal or trimming efficiency drops.
Ohio State University Extension notes that handheld trimmers can throw objects from their spinning action, so the guard and deflector shields are critical safety features. Ohio State recommends keeping bystanders at least 50 feet away because of thrown objects.
Choosing the correct line diameter
The Greenworks 24V trimmer manual states clearly: “Use only with the nylon cutting line of 0.065″ (1.65 mm) diameter.” The troubleshooting table lists heavy cutting line as a cause of trouble and gives the same fix: use only the specified 0.065-inch nylon line. Always check your own trimmer’s manual for the exact diameter and material. For more on matching line to your trimmer type, see our string trimmer buying guide.
Loading and replacing trimmer line
The Greenworks manual provides a step-by-step procedure for replacing the cutting line on its bump-feed head. First, remove the battery pack. Push the tabs on the sides of the trimmer head at the same time to release the spool cover, then lift out the spool and the coil protection. Remove any remaining line.
Cut two pieces of nylon line, each about 3 meters long. Bend one end of each piece roughly a quarter of an inch (6.35 mm) and insert the bent ends into the anchor holes on the spool. Wind both lines tightly around the spool in the direction indicated by the arrows, keeping the windings neat and below the spool’s edge. Place the lines in the guide slots, then set the spring into the spool housing and drop the spool back in. Feed the line ends through the holes in the housing, snap the spool cover back on, and pull the lines so about 15 centimeters extend from the slots. The manual notes that you can also replace the entire spool and cover as a unit if you prefer.
Adjusting cutting diameter and advancing line
The Greenworks trimmer is factory-set to a 12-inch (305 mm) cutting diameter. You can change it to a 10-inch (254 mm) diameter by removing the battery, taking out the blade screws that hold the cut-off blade, turning the blade 180 degrees, and retightening the screws. The manual says the smaller diameter can give greater runtime, while the larger diameter covers more area per pass.
To advance the line during use, tap the trimmer head against the ground while the motor is running. The bump action releases more line from the spool, and the cut-off blade trims the excess to the set diameter. The manual advises advancing line whenever you hear the engine speed increase or notice that the trimmer is cutting less efficiently.
Safety when operating a string trimmer
Ohio State University Extension recommends inspecting the work area before you start and removing all visible stones, sticks, wires or other debris. Because trimmers can fling objects, keep bystanders at least 50 feet away. Wear safety glasses with side shields or goggles, and consider adding a face shield for extra protection. Leather gloves, sturdy work boots (steel-toed if possible), long pants and a snug-fitting long-sleeved shirt help shield your skin from flying debris and contact with the spinning line.
The Greenworks manual also instructs users to wear protective gloves and safety glasses, and to keep hands and feet away from moving parts. Both sources stress that the guard must be in place and that safety features should never be overridden. If your trimmer can accept rigid brush-cutting blades, Ohio State cautions not to cut near hard objects when using those blades.
Maintenance and storage
After each use, the Greenworks manual says to clean the machine with a moist cloth and a neutral detergent. Do not use aggressive solvents or spray water onto the motor or electrical components. Keep the trimmer head free of grass, leaves and excessive grease, and make sure the air vents stay clear to prevent overheating. The cut-off blade can be sharpened with a file if it becomes dull and no longer cuts the line cleanly.
Ohio State University Extension emphasizes following the maintenance schedule in the owner’s manual. For gas-powered trimmers, that includes draining the fuel tank and running the engine until it stops before extended storage. For a battery-powered model like the Greenworks unit, remove the battery pack and store the trimmer in a cool, dry place out of reach of children. Secure the machine during transport to prevent damage. For a broader look at upkeep, read our string trimmer maintenance guide.
What the Greenworks 24V 12-inch trimmer manual says about line
| Topic | Guidance from the operator manual |
|---|---|
| Line diameter | 0.065 inch (1.65 mm) nylon only |
| Cutting path settings | 12 inches (305 mm) or 10 inches (254 mm) by rotating the cut-off blade 180° |
| Line advance method | Bump feed: tap the head on the ground while running |
| Line replacement length | Two pieces, each about 3 meters long |
| Spool replacement | Push tabs, remove spool cover, swap spool or rewind line |
| Cut-off blade | Continuously trims line; can be sharpened with a file |
| Cleaning | Moist cloth with neutral detergent; keep vents clear; do not spray water on motor |
Frequently asked questions
What size trimmer line should I use?
Always follow the specification in your trimmer’s manual. For the Greenworks 24V 12-inch cordless trimmer, the manual requires 0.065-inch (1.65 mm) nylon line. Its troubleshooting table lists heavy cutting line as a cause of problems.
How do I advance the line on a bump-feed trimmer?
While the trimmer is running, lightly tap the trimmer head on the ground. The mechanism releases more line, and the cut-off blade on the guard trims it to the correct length. Advance the line when the motor sounds faster or cutting performance drops.
Can I use a blade instead of trimmer line?
Some trimmers accept brush-cutting blades, but you must use attachments only as the manufacturer designed. Ohio State University Extension warns not to cut near hard objects when using rigid blades, and to keep the blade guard in place. Check your trimmer’s manual to see which heads and blades it accepts.
For more on choosing and using string trimmers, see our String Trimmers & Edgers category page.
