The basic steps: remove the spool, wind new string, and reinstall

To replace the string on a Greenworks 40V trimmer, you unscrew the spool cap at the trimmer head, remove the empty spool, wind new string into the spool grooves, and screw the cap back on. The whole job takes about five minutes once you have the right string diameter — almost all Greenworks 40V models use 0.065-inch string, though some older models use 0.080-inch. Check your manual or the spool itself to confirm which one you need before you buy.

You do not need to remove the battery or unplug anything. The trimmer head is at the end of the shaft, and the spool sits inside a plastic housing. The cap twists off by hand or with a wrench, depending on your model year.

Key Takeaways

  • Greenworks 40V trimmers almost always use 0.065-inch string diameter, but check your manual or the old spool to be certain before buying new string.
  • The spool cap unscrews by hand or with a wrench — if it is stuck, soak it with penetrating oil for ten minutes and try again.
  • Wind the string into both grooves on the spool in the direction marked by the arrow, leaving about six inches loose on each side.
  • Thread the loose ends through the eyelets in the trimmer head housing before screwing the cap back on, or the string will not feed out.

What string to buy and where to find it

Greenworks sells its own replacement spools pre-wound and ready to install — the part number is usually 25062 or 25062A depending on your model. A pre-wound spool costs between eight and twelve dollars and takes thirty seconds to swap in. If you want to wind your own string, buy a spool of 0.065-inch trimmer line from any hardware store or online retailer; a pound spool costs three to five dollars and will last through dozens of refills.

Pre-wound spools are simpler if you have never done this before. Winding your own saves money over time, but the first time you do it the process feels fiddly. Either way, do not buy string thicker or thinner than what your trimmer is designed for — the wrong diameter will not feed properly or will break constantly.

How to remove the old spool

Locate the spool cap at the very end of the trimmer head. On most Greenworks 40V models, the cap is a round plastic piece with a center bolt. Some caps unscrew by hand; others have a flat edge that requires a wrench or adjustable pliers to turn. If the cap is stuck, spray it with penetrating oil (like WD-40) and wait ten minutes before trying again.

Once the cap comes off, the spool will either fall out or pull out with a gentle tug. Set the cap and spool aside. Look inside the trimmer head housing and you will see two eyelets — small holes where the string exits. These are important: you will thread the new string through them later.

How to wind string onto the spool

If you are using a pre-wound spool, skip this section and go straight to reinstalling. If you are winding your own, cut a length of string about fifteen to twenty feet long. Look at the spool and you will see two grooves running around it, usually marked with an arrow showing which direction to wind.

Start at the center of the spool and wind the string into one groove, following the arrow direction. Wind it tightly and evenly, keeping tension on the string as you go. When you reach the outer edge of that groove, move to the second groove and wind it the same way. You should end up with about six inches of string loose on each side — do not wind it all the way to the end.

If your spool has a notch or slot at the edge, tuck the loose ends into it to hold them in place while you reinstall the spool. If there is no notch, just hold the ends with your fingers.

How to reinstall the spool and thread the string

Slide the spool back into the trimmer head housing. Make sure it sits flat and does not tilt. Now take the two loose ends of string and thread each one through an eyelet in the housing — one end through each hole. Pull the string through until you have about two to three inches sticking out of each eyelet.

Screw the cap back on, turning it by hand or with a wrench until it is snug. Do not over-tighten; you only need it tight enough that it does not come loose during use. Once the cap is on, the string should feed out automatically the next time you bump the trimmer head on the ground, or you can manually pull a little more string out of each eyelet if needed.

Troubleshooting if the string does not feed

If you turn on the trimmer and the string does not spin or feed out, the most common cause is that the loose ends are not threaded through the eyelets. Take the cap off, check that both string ends are going through the holes in the housing, and reinstall the cap.

If the string is threaded correctly but still will not feed, the spool may be wound too tightly or in the wrong direction. Remove the cap again and check that you wound the string following the arrow on the spool. If the arrow points clockwise, wind clockwise; if it points counterclockwise, wind that way. Rewind if necessary and try again.

If the string feeds but breaks constantly during use, you probably have the wrong diameter. Check your manual and confirm whether you need 0.065-inch or 0.080-inch string. Using the wrong size will cause feeding problems and breakage.

How often to replace the string

You will know it is time to replace the string when the cutting head gets noticeably shorter — usually after two to four hours of regular trimming, depending on how much thick brush you are cutting. Some people wind a new spool every season; others refill two or three times per season. If you use the trimmer weekly on a small yard, you might only need to refill once or twice a year.

Keep a spare spool or a spool of string in your garage so you are not caught without one when the current string runs out. Pre-wound spools are convenient for this because they are ready to go the moment you need them.

Frequently Asked Questions

Can I use a different brand of string on my Greenworks trimmer?

Yes. Any 0.065-inch trimmer string will work, as long as the diameter matches what your trimmer is designed for. Greenworks brand string is convenient, but third-party string from other manufacturers costs less and performs the same way. The key is getting the diameter right.

What if I wind the string in the wrong direction?

The string will not feed out properly. If you realize you wound it backwards, unwind it and wind it again following the arrow on the spool. It only takes a minute to fix, and it is worth doing right the first time.

Do I need to remove the battery before replacing the string?

No. The battery can stay in the trimmer while you replace the string. There is no risk of the trimmer turning on accidentally during this job, and you do not need to disconnect anything.

How much string do I need to buy if I am winding my own?

A one-pound spool of 0.065-inch string will fill your trimmer head many times over — usually twenty to thirty refills depending on how much string you use per job. One pound spool is the most practical size for home use and costs three to five dollars.

What if the spool cap is stuck and will not unscrew?

Spray the cap with penetrating oil and wait ten minutes. Then try again with a wrench or adjustable pliers. If it is still stuck, tap the wrench gently with a hammer to help break the corrosion loose. Do not force it hard enough to crack the plastic.