Direct Answer: To put line on a weed wacker, disconnect the spark plug wire for safety, then remove the spool housing by unscrewing the center bolt or pressing release tabs. Remove old line from the spool, measure and cut new line to the correct length (typically 15–20 feet for dual-line systems), then thread it through the guide slots on the spool. Wind the line tightly in the direction shown by the arrow, leaving 6–12 inches extending from each slot. Reinstall the spool, thread the line ends through the eyelets in the housing, and reassemble. For bump-feed or automatic systems, use shorter line lengths (6–12 inches per side) that feed as needed.

Understanding Your Weed Wacker’s Line System

Three types of weed wacker line-feed systems

Before you begin replacing your trimmer line, it helps to understand the equipment you’re working with. Weed wackers, also called string trimmers or weed eaters, use a spinning head with cutting line to trim grass and light vegetation. The line wears down over time and eventually breaks or becomes too short to cut effectively. Knowing your trimmer’s line-feed system will determine how much line you need and how you’ll install it.

Types of Line-Feed Systems

Most residential weed wackers use one of three line-feed systems:

  • Bump-feed systems: You manually advance new line by tapping (bumping) the spool head on the ground while the trimmer is running. This releases pre-measured line from the spool. Bump-feed is common on entry-level and mid-range trimmers.
  • Automatic line-feed systems: Line advances automatically as it wears down, without user intervention. These systems are convenient but require shorter initial line lengths and specific spool designs.
  • Manual line-advance systems: You manually pull line out as it wears. Less common on modern trimmers, these require careful length management to avoid tangles.

Check your trimmer’s manual or the spool housing label to identify which system your model uses. This determines how much line to load and affects installation technique.

Line Types and Diameter

Trimmer line comes in various diameters, typically ranging from 0.065 inches to 0.105 inches. Using the correct diameter for your trimmer is essential—lines that are too thin may break under load, while lines that are too thick won’t fit through the spool guides. Your trimmer’s manual specifies the correct diameter. Common sizes include 0.080 inches and 0.095 inches for residential models. Line is available in round, twisted, and serrated profiles; round line is most common and works well for most residential trimming tasks.

Safety Precautions Before Starting

Working on your weed wacker’s cutting head involves the spinning spool and sharp line edges, so safety comes first.

  • Disconnect the spark plug wire. This is the most critical step. Removing the wire from the spark plug prevents the engine from accidentally starting while you’re working on the head. Even brief contact with a spinning spool can cause serious cuts or lacerations.
  • Allow the engine to cool. If you’ve been using the trimmer, wait at least 10–15 minutes for the engine to cool before handling the spool housing.
  • Work on a flat, stable surface. Set the trimmer on a sturdy workbench or table to keep both hands free and maintain steady control.
  • Wear work gloves. Trimmer line has sharp cut edges. Gloves protect your hands from cuts while handling old or new line.
  • Use proper tools. Depending on your spool type, you may need a screwdriver, wrench, or nothing at all (if your model has quick-release tabs). Using the correct tool prevents stripping bolts or damaging the housing.

Accessing and Removing the Spool

Spool housings vary by manufacturer, but the removal process follows one of two main approaches.

Screw-Type Spool Housing

Many trimmers use a center bolt or screw to hold the spool housing in place:

  1. Locate the center bolt on the spool head. It’s usually labeled with directional arrows indicating which way to turn to loosen it.
  2. Using the appropriate screwdriver or wrench, turn the bolt counterclockwise (lefty-loosey). The direction may vary—check your manual if you’re unsure.
  3. Once loose, unscrew the bolt by hand and set it aside in a safe place where you won’t lose it.
  4. Carefully lift off the spool housing cover. The spool itself may stay attached or may come free depending on your model.
  5. If the spool is separate, lift it out of the housing.

Quick-Release Spool Housing

Some modern trimmers feature quick-release tabs that eliminate the need for tools:

  1. Locate the release tabs on the sides of the spool housing (usually two tabs on opposite sides).
  2. Press both tabs simultaneously, or press one and rotate slightly—the exact method varies by model.
  3. The housing cover should pop off or separate easily.
  4. Remove the spool.

Removing Old Line

Once the spool is out, remove any remaining old line. Most of the old line will pull away easily. Use a small brush or compressed air to clear dried grass clippings, dirt, or debris from the spool surface and guide slots. A clean spool ensures the new line winds evenly and feeds properly. Wipe the spool with a dry cloth before proceeding.

Measuring and Preparing New Line

Correct line length prevents tangling, ensures proper feeding, and reduces waste.

Finding the Right Length

Your trimmer’s manual specifies the correct line length for your model. As a general guideline:

  • Dual-line bump-feed systems: 15–20 feet total (7.5–10 feet per slot)
  • Dual-line automatic systems: 6–12 feet total (3–6 feet per slot)
  • Single-line systems: 8–15 feet

If your manual is unavailable, measure the spool diameter and check the manufacturer’s website or call customer service. Using too much line causes tangles and winding difficulty; too little means insufficient cutting length.

Cutting and Preparing Line

Trimmer line is sold in bulk spools or pre-packaged lengths. If buying bulk line:

  1. Measure the required length using a tape measure.
  2. Mark the line at the correct length using a pen or marker.
  3. Cut the line with scissors or a sharp utility knife. Make a clean, straight cut to prevent fraying.
  4. If the cut end is frayed, carefully trim away loose strands or briefly pass the end near a lighter flame to melt and seal it (be careful not to inhale fumes or burn yourself).

Some people prefer to pre-cut two equal lengths before winding, which simplifies the threading step.

Threading and Winding Line on the Spool

This is the most critical step. Improper winding causes line to tangle, break, or feed incorrectly.

Understanding Winding Direction

Look at your spool. Most spools have an arrow or directional marking indicating the correct winding direction—this is crucial. The line must wind in the direction the spool rotates when the trimmer runs. Winding backward causes line to tangle or fail to feed. Check your manual or look for printed arrows on the spool itself.

Threading Dual-Line Systems

Most residential trimmers use two lines, one in each side of the head:

  1. Locate the guide slots. The spool has two guide slots (small grooves) where the line sits. These slots guide the line as it winds and prevent tangling.
  2. Insert one end of your line into the first slot. Push the line into the slot until it seats firmly in the groove.
  3. Begin winding tightly. Wind the line around the spool in the direction indicated by the arrow. Keep tension on the line with your free hand to ensure tight, even wrapping. Loose winding causes the line to shift or tangle when installed.
  4. Wind in a spiral pattern. As you go around the spool, gradually work your way across so the line fills the spool width evenly. Avoid overlapping wraps or leaving gaps.
  5. Stop when you’ve wound the required length. For bump-feed systems, typically leave 6–12 inches of line extending from the spool. For automatic systems, refer to your manual (often 3–6 inches per side).
  6. Secure the first line. Tuck the end into the slot notch or slot to prevent unwinding.
  7. Repeat with the second line in the other slot. Thread the second line end into the second slot and wind in the same direction and with the same technique. Wind the same amount of line so both sides are balanced.

Winding Tension Tips

Wind tightly but not excessively. Tight winding prevents shifting and tangling. If you wind too tight, you may have difficulty reinstalling the spool or the line may break when feeding. If you wind too loosely, the line will shift inside the housing and cause feeding problems. Aim for firm, consistent tension—if you can easily twist or move the wound line by hand, it’s too loose.

Reinstalling the Spool and Testing

Proper reassembly ensures the line feeds correctly and the trimmer operates safely.

Threading Line Through the Eyelets

The spool housing has two small eyelet openings where the line exits the head:

  1. Hold the spool with the wound line facing up.
  2. Take one line end and thread it through the first eyelet opening in the housing. The line should pass straight through without kinks.
  3. Thread the second line end through the second eyelet.
  4. Ensure both lines are roughly equal length extending from the housing.

Reinstalling the Spool

For screw-type housings:

  1. Position the spool inside the housing, ensuring the line ends exit through the eyelets.
  2. Align the spool housing cover with the base housing.
  3. Insert the center bolt and turn it clockwise to tighten. Tighten firmly but do not overtighten, which can strip the bolt or crack the housing.
  4. Give the spool a gentle spin by hand to verify it rotates freely without resistance or rubbing.

For quick-release housings:

  1. Position the spool inside the housing with line ends exiting the eyelets.
  2. Align the cover and press down on the release tabs until you hear or feel a click, indicating the cover is seated.
  3. Test the spool by hand to ensure it spins freely.

Final Checks Before Use

Before running the trimmer:

  • Verify both line ends are even and extend to approximately the same length (typically 2–4 inches beyond the guard for bump-feed systems).
  • Check that the spool spins freely without catching or rubbing.
  • Reconnect the spark plug wire.
  • Run the trimmer briefly at low speed in an open area, away from people and objects. Listen for unusual noises and observe line feeding.
  • If line doesn’t feed or feeds unevenly, stop immediately and recheck your installation.

Troubleshooting Common Installation Issues

Line Won’t Feed Properly

Causes: Line wound backward (opposite the arrow), line wound too loosely, or line tangled inside the head.

Fix: Remove the spool and inspect the winding direction against the arrow. Rewind if necessary, ensuring tight, even wrapping. Check for tangles or debris inside the housing and clear them out.

Line Breaks Immediately After Use

Causes: Line diameter too thin for your trimmer, line wound too tightly causing stress, or line rubbing against sharp edges inside the housing.

Fix: Confirm you’re using the correct diameter (check your manual). If diameter is correct, rewind with slightly less tension. Inspect the spool and housing for sharp edges or burrs; smooth them with fine sandpaper if present.

Spool Head Vibrates or Makes Noise

Causes: Spool not seated properly, line wound unevenly, or spool housing not tightened correctly.

Fix: Remove the spool and reinstall it, ensuring the housing cover is fully seated and the center bolt is tight (but not over-tight). Check that line is wound in an even spiral without gaps or overlaps. If vibration continues, the spool may be damaged and require replacement.

Too Much Line Left Over

Causes: Measured or wound more line than needed.

Fix: For future use, confirm the correct length in your manual before winding. Leftover line can be saved for the next replacement; store it in a sealed bag to prevent drying and brittleness.

Frequently Asked Questions

How often should I replace the line on my weed wacker?

Line lifespan depends on usage frequency and terrain. Light residential use may require line replacement every 3–6 months, while heavy use might need monthly or more frequent replacements. You’ll know it’s time when the line becomes noticeably shorter, breaks frequently, or fails to cut effectively. Many people keep spare line on hand for quick changes.

Can I use any trimmer line on my weed wacker?

No. You must use the diameter and type specified in your trimmer’s manual. Using incorrect diameter line can damage the spool, cause poor feeding, or create safety hazards. If your manual is lost, contact the manufacturer with your model number, or consult an authorized dealer to confirm the correct specifications.

Why does my line keep tangling inside the spool?

Tangling usually results from winding in the wrong direction (opposite the arrow), winding too loosely, or poor spiral technique. Verify the arrow direction on your spool, wind with firm consistent tension, and wrap the line in an even spiral pattern without overlaps. If tangles persist, you may have a damaged or misaligned spool requiring replacement.

How much line should stick out of the trimmer head?

For bump-feed systems, line typically extends 2–4 inches beyond the cutting guard. Too much line wastes material and can cause uneven cutting or vibration; too little reduces cutting width. Check your manual for the exact specification, as designs vary. For automatic systems, much shorter line (0.5–1 inch) is typical since the system feeds automatically.

What should I do if I can’t get the spool cover off?

If a screw-type housing is stuck, apply penetrating oil (like WD-40) around the bolt and wait 15 minutes to loosen corrosion. Use the correct-sized screwdriver or wrench to avoid stripping. For quick-release tabs, ensure you’re pressing both tabs simultaneously and evenly. If the cover remains stuck, consult your manual or contact the manufacturer—forcing it may damage the housing.

Key Takeaways

Installing new line on your weed wacker is a straightforward maintenance task that extends the life of your trimmer and keeps it cutting efficiently. The process involves disconnecting the spark plug for safety, removing the spool, cleaning old line away, measuring and cutting new line to the correct length, winding it tightly in the direction indicated by the spool arrow, and reinstalling the spool with line threaded through the eyelets. Taking time to wind evenly and tightly the first time prevents most common problems. If your trimmer seems to have issues after installation—line not feeding, breaking, or unusual vibration—most problems can be solved by removing the spool and rewinding with correct technique. With practice, the entire process takes just 10–15 minutes.