Quick Answer
To restring a weed trimmer, identify your trimmer type (bump feed, automatic, or fixed spool), remove the trimmer head, clear out old string, measure the correct length for your model (typically 15–20 feet), thread new string into the spool following directional arrows, wind it tightly and evenly, and reassemble the head. The exact procedure varies by manufacturer, but these universal steps apply to most residential trimmers.
Identifying Your Trimmer Type
Before you start restringing, you need to know what type of spool system your trimmer has. This determines which restringing method applies to your specific machine.
Bump feed spools are the most common on residential trimmers. They feature a spool that advances string automatically when you tap the trimmer head against the ground. String winds around the spool in a specific pattern, and the system bumps a release lever to feed out fresh line as it wears.
Automatic feed systems use a spring-loaded mechanism that continuously advances string as it shortens. These require minimal user adjustment and are common on newer trimmer models. The string feeds out gradually without the bump action.
Fixed spool systems require manual advancement. You manually pull out new line as the old line wears or breaks, then manually cut it to length. These are less common on modern residential equipment but still found on some commercial-grade and older models.
Check your trimmer’s manual or look at the trimmer head design. Bump feed spools typically have a visible button or tap zone on the bottom. Automatic spools look similar but have a spring mechanism inside. Fixed spools show two separate line sections that you manually feed.
Tools and Materials You’ll Need
Gather these items before starting your restringing project:
- Replacement trimmer string — Check your trimmer’s manual or head for the correct gauge. Common sizes are 0.065 inch, 0.080 inch, and 0.095 inch diameter. Thicker gauges work better for tougher weeds and thicker brush.
- Screwdriver — Phillips or flathead, depending on your trimmer head fasteners.
- Needle-nose pliers or wire cutters — Helpful for removing old string and managing new line.
- Measuring tape — To ensure you cut the correct length of new string.
- Work surface — A clean table or workbench makes the job easier.
- Safety glasses — Protect your eyes from spring tension when opening the spool.
Most trimmers use 0.065 to 0.095 inch nylon string. Using the wrong gauge can cause feeding problems or reduce cutting performance. Premium commercial-grade string lasts longer but costs more than basic nylon alternatives.
Accessing the Spool: Removing the Trimmer Head
Your first step is safely accessing the spool inside the trimmer head. How you do this depends on your head design.
Screw-on heads have a cap that twists counterclockwise to remove. Grip the trimmer firmly with one hand and turn the cap with the other. If it’s stuck, try wrapping a rubber band or cloth around the cap for better grip. Once removed, you’ll see the spool inside.
Snap-on heads use a button or lever you press to release the head. Press the button and pull the head straight down and off the trimmer shaft. These are faster to remove but require you to note the orientation before removing so you can reassemble correctly.
Multi-part heads may have separate upper and lower sections. Remove the outer casing first, then access the spool inside. Be aware that springs may be under tension — remove these carefully and set them aside safely so they don’t get lost.
Some trimmers have a retaining collar that holds the spool in place. This typically unscrews or slides off. Set all small parts in a container so you don’t lose them during cleaning or restringing.
Removing Old String and Cleaning the Spool
Once the head is open, remove any remaining old string from the spool. Use needle-nose pliers or wire cutters to pull out stubborn pieces. Clean out dried grass, dirt, and debris with a dry cloth or soft brush.
Inspect the spool for cracks or damage. If the spool is cracked or has deep gouges, it may need replacement. Check that the spool spins freely on its center post. If it’s stuck or rough, the spool assembly may need replacing.
Look for directional arrows molded into the spool. These show the direction string should wind. This is critical — winding string in the wrong direction prevents proper feeding. Take a photo of these arrows if they’re unclear so you remember the correct direction while winding.
Measuring and Preparing New String
Cut the correct length of new string before winding. Most residential trimmers use 15–20 feet of string per spool. Check your trimmer’s manual for the exact recommendation, or follow this rule of thumb:
- For small residential trimmers (electric or 25–30 cc gas): 15 feet
- For mid-size residential trimmers (35–50 cc gas): 18–20 feet
- For larger residential or semi-commercial trimmers: 20–25 feet
Measure the string carefully using a tape measure or by laying it out against a known reference. Cut cleanly with scissors or a utility knife — a jagged end makes threading harder. Some people melt the ends slightly with a lighter to prevent fraying, though this isn’t required for most applications.
Before winding, check that your new string is the same gauge as specified in your manual. Mixing gauges can cause feeding problems and uneven cutting performance.
Threading String on Bump Feed Spools
Bump feed spools are the most common type on residential trimmers. Here’s the step-by-step process:
- Locate the anchor notch. Look for a small notch or slot on the outer edge of the spool where you insert one end of the string. This usually has a small arrow indicating where to start.
- Insert the first end. Push one end of your cut string into the anchor notch and pull it tight so it’s seated securely. This end stays in place while you wind.
- Wind the string tightly. Following the directional arrows on the spool, wind the string in neat, overlapping coils around the spool. Keep tension even and avoid crossing the line over itself. Wind from the anchor notch outward and around, filling the spool evenly.
- Wind until nearly full. Continue winding until the spool is nearly full, leaving a small lip of spool visible at the edge. Don’t overfill — this prevents proper head closure and can jam the mechanism.
- Locate the exit notch. Most bump feed spools have a second notch on the outer edge where the end of the string exits. Tuck the end of the string into this notch so it doesn’t unwind.
- Check your work. The string should be evenly wound with no crossing or bunching. It should lay flat against the spool with consistent spacing between coils.
Common mistakes: winding too loose (string doesn’t feed properly), winding in the wrong direction (prevents feeding), overfilling (head won’t close), or not seating the anchor end securely (string slips during operation).
Threading String on Fixed Spool and Automatic Feed Systems
Fixed spool and automatic feed systems use different winding patterns than bump feed spools.
Fixed spool systems typically have two separate chambers on the spool, one for each string line. String runs from the center of the spool outward through each chamber. Here’s the process:
- Insert one end of string into the first chamber’s center hole.
- Wind the string around the chamber in the direction of the arrow.
- When the first chamber is full, move to the second chamber.
- Insert the second string end and wind it in the same direction around the second chamber.
- The two string ends exit the center of the spool head.
Automatic feed systems typically have a single spool with a spring mechanism underneath. Wind the string similarly to a bump feed system (around the spool following directional arrows), but automatic spools usually require less string (10–15 feet total) since the spring mechanism feeds line continuously. Wind until the spool is about three-quarters full, then seat the string end in the exit notch.
Consult your trimmer’s manual for your specific automatic system, as designs vary. Some automatic spools require the string to wind in a figure-eight pattern or have multiple chambers.
Winding and Reassembling the Trimmer Head
Once the string is wound, you’re ready to reassemble the head.
Check the spool one final time. Ensure the string is wound tightly and evenly with no gaps or overlapping. Loose winding causes tangling and poor feeding. The string should lay flat against the spool with even spacing between coils.
Reassemble the head components. If your head has an upper and lower section, align them carefully before screwing or snapping them together. Make sure any springs or tension mechanisms are positioned correctly.
Attach the head back to the trimmer. For screw-on heads, twist clockwise until snug — don’t over-tighten, which can strip the threads. For snap-on heads, align the head with the shaft and push down firmly until you hear or feel a click.
Pull out the string ends. Once reassembled, gently pull each string end through the exit openings. The string should pull through smoothly with no resistance. If it snags, the spool may not be wound correctly — remove the head and rewind.
Trim the string to length. Once both ends are extended, trim them to the proper cutting length for your trimmer head. Most residential heads use about 8–10 inches on each side, but check your manual. The exact length depends on your head design and cutting disc diameter.
Test before use. Before operating the trimmer, check that the string rotates freely by hand. Spin the spool gently — it should turn smoothly with no resistance or grinding sounds. Listen for any unusual noises, which indicate improper assembly.
Troubleshooting Common Restringing Problems
String won’t feed properly after restringing. This usually means the string was wound in the wrong direction or too loosely. Remove the head and check the directional arrows on the spool. Rewind the string following the arrows precisely. Ensure each coil is tight and even with no gaps.
String keeps breaking or tangling immediately. Broken string often results from winding it too tightly or incorrectly seating the anchor end. Verify the string gauge matches your manual — using the wrong gauge causes premature breaking. If tangling occurs, the spool is likely overfilled. Rewind using slightly less string.
The trimmer head won’t close properly. This indicates the spool is overfilled. Remove the head, unwind some string (leaving about half an inch of spool lip visible), and reassemble. The head should close smoothly with gentle pressure.
String doesn’t extend far enough. You may not have cut the string long enough. Remove the head, add more string, and rewind. Alternatively, you may have trimmed the cut ends too short after reassembly. Extend the string further and test.
String keeps slipping or unwinding. The anchor or exit notch may not be holding the string securely. Check that the string ends are fully seated in their notches. On some spools, you can use a small dab of adhesive (like a tiny drop of super glue) on the notch to keep the string from slipping, though this makes future restringing harder.
The spool won’t spin smoothly. Debris may be blocking the center post. Remove the spool and clean around the center post and pivot point. Apply a tiny amount of light machine oil if the spool is still rough, then wipe away excess. Avoid over-oiling, which attracts dirt.
Frequently Asked Questions
How often should I restring my weed trimmer?
Restringing frequency depends on usage and terrain. Light residential use (30 minutes weekly on well-maintained lawn) may require restringing every 2–3 months. Heavy use on thick brush or overgrown areas may need restringing monthly or more frequently. You’ll know it’s time when the string wears noticeably shorter or breaks repeatedly during use.
Can I use any type of trimmer string on my trimmer?
No — always use the gauge specified in your trimmer’s manual. Using incorrect gauge causes feeding problems, breakage, or reduced cutting performance. Common gauges are 0.065, 0.080, and 0.095 inches. Specialty string types (twisted, spiral, or reinforced) may also be available for your model. Check your manual or trimmer head for the correct specification before purchasing replacement string.
What’s the difference between bump feed and automatic feed?
Bump feed requires you to tap the trimmer head against the ground to advance fresh string as it wears. Automatic feed uses an internal spring mechanism that continuously advances string without bumping. Automatic systems are more convenient but typically require restringing more frequently since they feed string constantly. Bump feed gives you more control and uses less string per session.
Why does my string keep breaking even after restringing?
String breakage can result from several causes: incorrect gauge (too thin for your needs), winding too tightly, debris inside the spool blocking smooth feeding, worn cutting disc edges causing friction, or operating the trimmer at full throttle on thick brush. Try using a thicker gauge string, ensure the spool is wound loosely enough to feed smoothly, and check that the cutting disc edges are smooth and not chipped.
