The basic steps: remove the spool, wind new string, and reinstall
To replace the string on a Greenworks 80V trimmer, you unscrew the spool cap at the trimmer head, remove the empty spool, wind new string around it in the correct direction, and screw the cap back on. The whole job takes about five minutes once you have the right string diameter — usually 0.065 inches for Greenworks models, though you should check your manual to be certain.
The string comes wound on a spool inside the trimmer head. As you use the trimmer, the string wears down and eventually breaks. Rather than buying a new trimmer head, you wind fresh string onto the existing spool and put it back. Greenworks sells pre-wound spools you can swap in directly, or you can wind string yourself onto a bare spool if you prefer to buy bulk string.
Key Takeaways
- Greenworks 80V trimmers use 0.065-inch string diameter, but check your manual because some models vary.
- You can buy a pre-wound replacement spool and swap it in without winding anything, which is the fastest option.
- If you wind string yourself, the spool has two slots or eyelets where the string anchors, and you must wind in the direction marked on the spool.
- The spool cap unscrews by hand or with a wrench depending on your model — check which before you start.
- New string costs between $5 and $15 per spool, and one spool typically lasts several hours of trimming.
What string diameter and type your Greenworks trimmer needs
Most Greenworks 80V models use 0.065-inch string, but some older or specialty models use 0.080-inch. Open your trimmer manual or look at the spool itself — the diameter is usually printed on the plastic. If you cannot find it, call Greenworks customer service with your model number, which is on a label on the battery or motor housing.
Buy string made for string trimmers, not fishing line or other cord. Greenworks sells its own branded spools, which fit perfectly and cost around $10 to $15 per spool. Aftermarket brands like Stens, Oregon, and Maxpower also make compatible string at similar prices. All of these are nylon and designed to withstand the heat and friction of the spinning head.
Option 1: Swap in a pre-wound spool (fastest method)
If you buy a pre-wound replacement spool, you skip the winding step entirely. Unscrew the spool cap on the trimmer head, pull out the old spool, and push the new one in until it clicks or seats. Screw the cap back on, and you are done. This takes two minutes and eliminates the chance of winding the string wrong.
Pre-wound spools cost slightly more than bulk string — usually $12 to $18 per spool instead of $5 to $10 — but the time saved and the certainty that the string is wound correctly make it worth the difference for most people. Greenworks sells them at hardware stores, online retailers, and directly from their website.
Option 2: Wind string yourself onto a bare spool
If you buy bulk string and a bare replacement spool, you wind the string yourself. Start by anchoring one end of the string in one of the two slots or eyelets on the spool — there is usually one slot on each side. Push the string into the slot until it catches, then wind the string tightly around the spool in the direction the arrow on the spool points. Wind until you have about 15 to 20 feet of string on the spool, then anchor the other end in the second slot.
The direction matters. If you wind against the arrow, the string will unwind as the spool spins, and you will run out of string in seconds. Look at the spool before you start — the arrow shows which way to wind. Some spools have a small bump or notch at the starting point to help you position the string correctly.
Bare spools cost $3 to $8, and bulk string costs $5 to $12 per spool depending on length and brand. If you trim regularly, buying bulk string and winding your own spools saves money over time, but it requires more effort each time you need to restring.
How to remove and reinstall the spool cap
The spool cap is the plastic or metal cover at the center of the trimmer head. On some Greenworks models, it unscrews by hand — grip it firmly and turn counterclockwise. On others, you need a wrench or socket to turn it. Check your manual to see which applies to your model, or try by hand first; if it does not budge after a firm grip, stop and get the right wrench rather than risk stripping the threads.
Once the cap is off, the spool should pull straight out. If it sticks, wiggle it gently side to side as you pull. Do not force it, because the spool can crack. Once the old spool is out, insert the new one — it should slide in smoothly and sit flat against the bottom of the head. Screw the cap back on by hand or wrench, turning clockwise until it is snug. Do not overtighten; snug is enough.
Threading the string through the trimmer head outlet
Once the spool is installed and the cap is on, you need to thread the string through the outlet hole in the trimmer head so it extends outward and can cut. The outlet is usually a small hole or slot on the side of the trimmer head. Pull a length of string from the spool and push it through the outlet until about 4 to 6 inches extends beyond the head on each side.
Some Greenworks models have a guide or notch that helps you position the string correctly. If your trimmer head has a small bump or line on the side, that is where the string should sit. Once the string is threaded and positioned, the trimmer is ready to use. The string will wear down as you trim, and the head will automatically feed more string as needed on some models, or you may need to manually advance it on others — check your manual for your specific model.
Troubleshooting common winding and installation problems
If the string unwinds as soon as you start the trimmer, you wound it in the wrong direction. Stop when ready, remove the spool, and rewind it in the opposite direction. Winding against the spool arrow is the most common mistake, and it makes the string useless.
If the spool cap will not unscrew, do not force it. Spray a small amount of penetrating oil like WD-40 around the threads, wait 10 minutes, and try again. If it still will not budge, you may have the wrong wrench size — try the next size up or down. If the cap threads are stripped and the cap spins without unscrewing, the trimmer head may need replacement, which costs $20 to $40.
If the string does not feed or advance as you trim, the spool may not be seated correctly. Remove the cap, take out the spool, and reinstall it, making sure it sits flat and clicks into place. If the problem persists, the feed mechanism inside the head may be worn, and the trimmer head will need replacement.
Frequently Asked Questions
Can I use a different diameter string than what my manual says?
No. Using thicker or thinner string can damage the trimmer head or cause the string to break when ready. The head is designed for a specific diameter, and using the wrong size stresses the feed mechanism and the motor. Always use the diameter your manual specifies.
How often do I need to replace the string?
It depends on how much you trim and what you are cutting. Light residential use — trimming edges once a week — might get 10 to 15 hours per spool. Heavy use or cutting thick weeds can wear a spool out in 5 to 8 hours. You will know it is time when the string breaks repeatedly or stops cutting cleanly.
What is the difference between a pre-wound spool and a bare spool?
A pre-wound spool comes with string already wound and ready to install. A bare spool is empty plastic, and you wind string onto it yourself. Pre-wound is faster and more foolproof; bare spools are cheaper if you buy bulk string and do not mind the winding step.
Do I need to remove the battery before replacing the string?
Yes. Always remove the battery before working on the trimmer head. Even though the trimmer cannot start without the battery, removing it is a safety habit that prevents accidental startup and is required by Greenworks safety guidelines.
Can I wind the string in a figure-eight pattern instead of a spiral?
No. The spool is designed for spiral winding in one direction. Figure-eight or random winding will cause the string to tangle, jam, or unwind unpredictably. Follow the arrow on the spool and wind in a single spiral direction.