The basic steps to load new string into your trimmer

Replacing weed eater string takes about five minutes once you know where the spool is and how your model releases it. Most trimmers use one of two designs: a fixed spool that you unwind by hand, or a cartridge that clicks out of the head. You'll need the new string (usually sold as a spool or pre-wound cartridge), scissors, and sometimes a small flathead screwdriver—check your trimmer's manual to see which.

The fastest way to find your exact steps is to search your trimmer's brand and model number plus "string replacement" on YouTube; manufacturers often post videos showing their specific head design. If you can't find a video, the manual usually comes as a PDF online. That said, the general sequence is the same across most brands: stop the engine, locate the spool or cartridge, remove the old string, wind or insert the new string, and reassemble.

Key Takeaways

  • Most trimmers have either a fixed spool you unwind by hand or a snap-out cartridge, and your manual will tell you which one you have.
  • The string diameter matters—common sizes are 0.065 inch, 0.080 inch, and 0.095 inch—and using the wrong size can jam the head or break the string.
  • Wind the string tightly and evenly in the direction marked on the spool, leaving the correct amount of string hanging out (usually 4 to 6 inches per side).
  • If your trimmer has a bump-feed head, you may not need to rewind anything—just snap in a new cartridge and you're done.

Finding and removing the spool or cartridge

Turn off the engine and let the trimmer cool for at least two minutes. Flip the trimmer upside down so you can see the cutting head clearly. Look for a large plastic cap or knob in the center of the head—this is either the spool cover or the cartridge itself.

If it's a fixed spool, you'll see a knob with a slot or arrow. Turn it counterclockwise (or in the direction the arrow points) until it comes free. The spool will stay attached to the head by a shaft. If it's a cartridge-style head, look for a small tab or button on the side—press it and the whole cartridge will pop out. Some cartridges twist out instead; your manual will show which.

Once the spool or cartridge is exposed, pull out any remaining old string. If string is wound tightly, you may need to gently pry it with a flathead screwdriver or your fingernail. Don't force it—if it won't budge, soak the head in warm water for a few minutes to soften any dried grass or debris.

Measuring and preparing the new string

Check your trimmer's manual or the spool cover for the correct string diameter. The most common sizes are 0.065 inch, 0.080 inch, and 0.095 inch. Using the wrong diameter can cause the string to jam in the feed hole or snap during use. If you've lost the manual, measure the old string with a ruler or calipers, or call the trimmer's manufacturer with your model number.

Cut a length of string about 15 to 20 feet long. If you're using a pre-wound cartridge, skip this step—the string is already loaded. For a fixed spool, you'll wind this string onto the spool yourself. Lay the string out straight on a clean surface so it doesn't tangle as you work.

Winding string onto a fixed spool

Look at the spool for an arrow or marking that shows the direction to wind. This is critical—winding the wrong way will cause the string to unravel when you run the trimmer. The arrow usually points clockwise or counterclockwise; follow it exactly.

Hold the spool in one hand and the string in the other. Insert one end of the string into the small notch or hole at the edge of the spool—most spools have a slot designed to hold the string end in place while you wind. Wind the string tightly and evenly across the spool, keeping tension so there are no loose loops or overlaps. Wind until you've used about 12 to 15 feet of string, leaving 3 to 5 feet unwound.

Once the spool is full, tuck the loose end into the slot or notch on the opposite side of the spool to hold it in place. This prevents the string from unwinding before you reinstall the spool. If your spool has two separate chambers (one for each cutting line), repeat the process on the other side with a second length of string.

Installing the spool or cartridge and threading the string

Slide the spool back onto the shaft in the trimmer head, making sure it sits flush and the notches or tabs align. Screw the cover knob clockwise until it's snug—don't over-tighten, as this can crack the plastic. If you're using a cartridge, straightforward snap it back into the head until you hear or feel a click.

Now pull the loose ends of string out through the feed holes on the sides of the head. These holes are usually small slots or openings near the edge. Pull gently until about 4 to 6 inches of string hangs out on each side. This is your cutting length—the trimmer will automatically feed more string as the ends wear down (on bump-feed models) or you'll trim it manually on fixed-length models.

If the string won't pull through the feed hole, the hole may be clogged with dried grass. Use a small straightened paperclip or a toothpick to clear it, then try again. Once both sides are threaded, you're ready to test the trimmer.

Testing and trimming the string to length

Before you use the trimmer on grass, run it for a few seconds in an open area away from people and pets. Listen for any grinding or rattling sounds, which would mean the string is rubbing against the head or the spool isn't seated correctly. If it sounds normal, the string should spin freely without wobbling.

Stop the engine and let it cool. Measure the string hanging from each side—it should be even on both sides and about 4 to 6 inches long, depending on your trimmer model. If one side is longer, trim it with scissors to match the other. Some trimmers have a plastic guard with a built-in cutting edge; you can use that to trim the string to the correct length by running the trimmer briefly and letting the guard do the work.

After the first few minutes of use, check the string again. It may have settled slightly or the spool may have shifted. Adjust if needed, and you're done.

Common mistakes and how to avoid them

Winding in the wrong direction is the most common error. The string will unravel when ready when you start the trimmer. Always check the arrow on the spool before you begin—if you're unsure, wind a foot or two, test it by hand to see if it holds, and unwind if it doesn't.

Using the wrong string diameter causes jams or breakage. Measure the old string or check your manual. If you buy string at a hardware store and aren't sure, ask the staff to measure it against a sample or bring the old string with you.

Leaving the string too long makes it drag on the ground and wear faster. Trim it to the length specified in your manual—usually 4 to 6 inches per side. Leaving it too short reduces cutting width and may not reach the guard, so the trimmer won't cut efficiently.

Not seating the spool or cartridge fully causes vibration and noise. Make sure the spool clicks or screws in completely and sits flush with the head. If it's loose, the string won't feed evenly.

Frequently Asked Questions

Can I use any brand of string in my trimmer?

Most string is universal as long as the diameter matches your trimmer's specifications. Check your manual for the correct size. Some trimmers use proprietary cartridges that only fit that brand, but loose string spools are usually interchangeable across brands.

How often do I need to replace the string?

It depends on how much you use the trimmer and the thickness of the vegetation. Light residential use might mean replacing string every few months; heavy use could mean every few weeks. You'll know it's time when the string is noticeably shorter, frayed, or breaks frequently during use.

What if the string won't feed through the head?

The feed hole is likely clogged with grass or debris. Turn off the trimmer, let it cool, and use a straightened paperclip or toothpick to gently clear the hole. If the string itself is kinked or damaged, cut off the damaged section and try again with a fresh end.

Do I have to wind the string myself, or can I buy it pre-wound?

Many brands sell pre-wound cartridges that snap directly into the head—no winding required. These cost more per use than bulk string, but they're faster and less error-prone. Check if your trimmer model supports cartridges; if it does, the manual will say so.

Why does my string keep breaking?

The most common causes are using the wrong diameter (too thin for your trimmer), winding it too loosely so it slips and tangles, or hitting rocks and hard objects. Make sure the diameter matches your manual, wind tightly and evenly, and try to avoid cutting near gravel or pavement.