How to Change String Trimmer Line: Complete Step-by-Step Guide
Changing string trimmer line takes 5–10 minutes once you’ve done it a few times. The process differs slightly between bump-feed heads (most common), fixed-line heads, and automatic-feed heads — but the core steps are the same: remove the spool, wind new line, and reinstall. Using the correct line diameter for your trimmer is critical — the wrong gauge damages the motor or cuts inefficiently.
What You’ll Need
- Replacement trimmer line (correct diameter — see below)
- Scissors or cutting blade
- Flat screwdriver (for some spool covers)
- Work gloves
- Your trimmer’s owner’s manual (for correct line diameter)
Safety Precautions
- Turn off and unplug (or remove the battery) before changing the line. Never work on a running trimmer head.
- Let a gas trimmer cool completely before handling the trimmer head area.
- Wear gloves. Trimmer line ends can be sharp after cutting, and the spool edges can cut your fingers.
- Use the correct line diameter. Oversized line jams the bump-feed mechanism and strains the motor; undersized line wears out immediately.
What Trimmer Line Size Do I Need?
| Line Diameter | Best For | Common on |
|---|---|---|
| 0.065″ | Light residential use, soft grass | Small lightweight trimmers |
| 0.080″ | Standard residential use | Most consumer trimmers |
| 0.095″ | Heavier residential, light weeds | Mid-weight trimmers |
| 0.105″–0.110″ | Heavy brush and thick weeds | Commercial-grade trimmers |
| 0.130″+ | Very heavy commercial use | Large-engine professional trimmers |
The correct diameter is printed on the trimmer head or in your owner’s manual. See our string trimmer line types guide for a full breakdown including line shapes and materials.
How to Change Bump-Feed Trimmer Line (Most Common)
Step 1: Remove the Spool
With the trimmer off and cool, press in the spool tabs on the sides of the trimmer head (there are usually two tabs opposite each other) and pull the spool cover off. On some models, you rotate the cover counterclockwise. Remove the inner spool — it’s a plastic cylinder with the line wound around it.
Empty any remaining old line by pulling it off the spool. Note the direction the old line was wound — most spools have an arrow indicating wind direction (clockwise or counterclockwise). Winding in the wrong direction causes the line to unspool immediately during use.
Step 2: Cut the New Line
Cut a length of new line approximately 20 feet long (for most standard spools). Some manufacturers specify a maximum length — longer than spec causes the line to jam in the feed mechanism. Check your manual. Pre-cut line packs are also available if you want to skip measuring.
Step 3: Fold and Insert the Line
Fold the 20-foot length in half to create two 10-foot strands. Find the notch or anchor hole in the center divider of the spool — insert the center fold into this slot/notch to lock it in place. Most spools have two separate winding chambers — one for each strand of line.
Step 4: Wind the Line onto the Spool
Wind both strands simultaneously in the direction indicated by the arrow on the spool (usually clockwise when viewed from below). Keep the line neat and tight — avoid crossing or overlapping strands, which causes the line to jam. Wind until about 6 inches of line remains free on each side.
Step 5: Route the Free Ends Through the Eyelets
Before reinstalling the spool, feed each free end of line through the corresponding eyelet (outlet hole) on the trimmer head. These are the small holes on the sides of the head through which the line exits. Pull the line through until the spool seats fully back in the head.
Step 6: Reinstall the Spool Cover
Press the spool cover back onto the head until the tabs click into place, or rotate clockwise to lock. Give both free line ends a gentle tug to confirm they’re seated correctly and feeding freely.
Step 7: Test the Bump Feed
Start the trimmer at a safe test location. Bump the head lightly on the ground — each bump should advance the line approximately 1 inch. If the line advances too much or won’t advance, remove the spool and verify the winding direction and that the line is properly routed through the eyelets.
How to Change Fixed-Line Trimmer Heads
Some trimmers — particularly commercial and professional models — use a fixed-line head where individual pre-cut lengths of line are inserted into holes in the head. The process is simpler:
- Pre-cut pieces of line to the length shown in the manual (usually 6–12 inches).
- Fold each piece in half and insert the fold into the receiving hole until it clicks or locks.
- Lines are replaced individually when they break during use.
How to Change Automatic-Feed Heads
Automatic-feed heads sense when the line gets short and advance more line automatically — no bumping required. Changing the spool on these is the same as bump-feed heads, but the spool itself is often sealed or pre-wound from the factory. Check if your brand sells pre-wound replacement spools (e.g., Black+Decker AFS, Toro Zip Tip) — these snap in and out in seconds with no winding required.
Troubleshooting Common Line Problems
| Problem | Cause | Fix |
|---|---|---|
| Line won’t advance when bumped | Crossed or overlapping windings | Rewind the spool more neatly |
| Line advances too fast | Line wound in wrong direction | Remove and rewind following the arrow |
| Line fuses inside spool | Heat welding from nylon-to-nylon contact | Soak spool in water for 30 min to separate; rewinding neatly prevents recurrence |
| Line breaks immediately on use | Wrong line diameter or brittle old line | Verify correct diameter; use fresh line from a sealed package |
| Trimmer head vibrates excessively | Uneven line lengths or missing line | Ensure both line strands are equal length |
Pro Tips
- Keep spare line in a sealed bag. Trimmer line dries out and becomes brittle when stored exposed to air and light. Seal unused line in a zip bag — it stays flexible and cuts better.
- Soak new line in water for 30 minutes before winding. This makes the line more flexible and significantly reduces breakage during use, especially in cold weather.
- Don’t over-wind. Loading too much line causes it to jam in the spool chamber. Follow the manufacturer’s maximum length specification.
- Use pre-wound replacement spools when available. If your trimmer brand sells pre-wound drop-in spools, they save time and produce consistent results. Worth the small extra cost.
Frequently Asked Questions
How do I know what size trimmer line I need?
Check the label on your trimmer head — it’s almost always printed there. You can also find it in the owner’s manual or search your trimmer model number online. Using the wrong gauge causes jamming (too thick) or excessive wear (too thin).
How long does a spool of trimmer line last?
A single standard spool (roughly 20 feet) lasts 1–3 mowing sessions for an average suburban yard, depending on trimming density and how often you bump-advance the line. Heavy use with lots of obstacles wears through line much faster than open-area trimming.
Why does my trimmer line keep breaking?
Common causes: hitting rocks or concrete edges (normal — use technique to avoid pavement), using line that’s too thin for the application, old/brittle line, or running the trimmer at maximum RPM into hard surfaces. See our trimmer line guide for the right line for your conditions.
Can I use any brand of trimmer line?
Yes — trimmer line is not brand-specific beyond diameter. Any quality trimmer line of the correct diameter will work in any brand’s head. Oregon, Arnold, Husqvarna, and Shakespeare are all quality replacement line brands available at most hardware stores.
What does “dual line” mean on a string trimmer?
Dual line means the trimmer head uses two strands of line simultaneously — one exits on each side. This cuts more material per revolution, making it more efficient on thick grass and weeds. Most standard bump-feed heads are dual line. Single-line heads are typically found on smaller, lighter trimmers.
Conclusion
Changing trimmer line is one of the basic skills every string trimmer owner needs. It takes 5–10 minutes once you know the process, and keeping a spare roll of the correct diameter in your shed means you’ll never lose trimming time to an empty spool.
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