Quick Answer: How to Install New Trimmer Line

To install new trimmer line, stop the trimmer and let it cool completely. Remove the spool by twisting counterclockwise or pressing release tabs (depending on your model). Identify your line gauge—typically 0.065″, 0.080″, or 0.095″—then wind the new line tightly around the spool in the direction shown by arrows on the spool. Leave 4–6 inches of line free, insert both ends into the eyelets on the trimmer head, and reinstall the spool by twisting clockwise until snug. Rotate the trimmer head to test; the line should unwind smoothly without tangling or binding.

Understanding Your Trimmer Type

Three types of trimmer spool systems displayed for comparison: twist-on, bump-feed, and sealed cartridge

Before you begin, identify which type of spool system your trimmer uses. This determines how you’ll remove and reinstall the spool, and affects the overall difficulty of the job.

Twist-On Spool Systems

Most residential string trimmers use a twist-on spool design. The spool threads directly onto the trimmer head and is secured by rotating it clockwise. Removal requires rotating counterclockwise by hand or with a wrench. This is the most common system on DeWalt, Echo, Ryobi, and Makita consumer models.

Bump-Feed Systems

Bump-feed trimmers advance line automatically when you tap the trimmer head against the ground. These use a spring-loaded spool with release tabs on either side. Instead of twisting, you press or pry the tabs outward to release the spool cartridge. Line feeds automatically as the spool rotates, reducing manual winding complexity but requiring precise tab alignment during reinstallation.

Sealed Cartridge Systems

High-end or commercial trimmers often use sealed cartridge systems where the entire spool assembly is disposable or permanently sealed. These typically require replacing the entire cartridge rather than rewinding line. Check your manual to confirm whether your trimmer supports line replacement or cartridge swap.

Identifying the Correct Line Gauge

Trimmer line comes in several diameters. Using the wrong gauge can cause feeding problems, reduce cutting efficiency, or damage your trimmer’s drive system.

Common Line Gauges and Applications

  • 0.065″ (1.6 mm): Lightweight, for thin grass and light weeds. Most common for battery-powered and compact trimmers.
  • 0.080″ (2.0 mm): Mid-weight, standard for residential gas and electric trimmers. Handles thick grass and moderate brush.
  • 0.095″ (2.4 mm): Heavy-duty, for thick weeds, brush, and woody vegetation. Common on commercial and high-power models.

Finding Your Trimmer’s Specifications

Check three places for the correct gauge:

  • Owner’s manual: Always the most reliable source. Lists the exact line diameter your trimmer is designed for.
  • Old spool or line packaging: The gauge is printed on the spool hub or the line packaging itself.
  • Trimmer head label: Many manufacturers print specifications directly on the head housing.

If you cannot find the specification and do not have the manual, contact the manufacturer with your model number, or visit the manufacturer’s website to download the manual.

Removing the Spool

Safety First

Before disassembling your trimmer, take these precautions:

  • Stop the trimmer and ensure the engine or motor has completely cooled (wait at least 10 minutes).
  • Disconnect the spark plug wire (gas models) or unplug the battery (electric models) to prevent accidental starting.
  • Wear work gloves to protect your hands from sharp line edges.
  • Set the trimmer on a clean, flat work surface with good lighting.

Removing a Twist-On Spool

  1. Locate the spool on the trimmer head. It is typically at the center where the cutting head rotates.
  2. Use your hand or a wrench to grip the spool hub firmly.
  3. Rotate the spool counterclockwise (lefty-loosey). Most spools unthread after 3–5 full rotations.
  4. Once loose, unscrew by hand until the spool comes free. Take note of any washers, springs, or spacers underneath; set them aside in a small container so they do not get lost.
  5. Examine the spool for damage (cracks, stripped threads) and replace if necessary.

Removing a Bump-Feed Spool

  1. Locate the release tabs on either side of the spool cartridge (usually plastic tabs protruding from the sides).
  2. Using a flathead screwdriver or your fingernail, gently pry or press both tabs outward simultaneously.
  3. The cartridge should pop out or slide out. If it resists, check that both tabs are fully depressed before pulling.
  4. Once removed, inspect the cartridge for cracks or a stuck spring mechanism. If the spring feels loose or the cartridge is cracked, replace it.

Winding New Line on the Spool

Preparing the Line

Purchase line in bulk (usually 100–150 feet per spool) rather than pre-wound cartridges, which are more expensive. You may need to cut the line to the correct starting length, typically 20–30 feet depending on your spool size and trimmer design. Check your manual for the recommended starting length.

Following Winding Direction

Examine the spool carefully for arrows or directional markings. These indicate the correct winding direction. Winding in the wrong direction causes the line to jam, tangle, or unwind improperly during operation.

  • Most clockwise-rotating spool heads require line to be wound counterclockwise on the spool (or vice versa, depending on design).
  • If the spool has two winding chambers (one on each side), wind each side in the direction indicated on the spool.
  • When in doubt, rewind in the opposite direction of the arrow markings on the spool hub.

Winding Technique

  1. Thread one end of the line into the starting notch or anchor point on the spool. This notch is typically a small groove or slot at the edge of the winding chamber.
  2. Hold tension on the line with your other hand to keep it taut as you wind.
  3. Wind the line tightly and evenly in the direction indicated, overlapping each pass slightly so the line does not pile up in one area.
  4. Continue winding until approximately 4–6 inches of line remain free (unwound). This free length prevents the spool from becoming too tight and allows enough line to feed into the eyelets.
  5. Secure the free end by tucking it into a slot or notch on the spool, or hold it in place by wrapping it loosely around the spool hub.

Common Winding Mistakes

  • Winding too loosely: Loose line tangles during operation and may not feed smoothly. Wind firmly so each pass sits snugly against the previous one.
  • Winding in the wrong direction: Always follow the arrow markings on the spool. Incorrect direction prevents proper line feeding and causes jamming.
  • Leaving too much free line: More than 6 inches of free line can catch on the spool housing or wrap around the drive shaft during operation, damaging the trimmer.
  • Leaving too little free line: Less than 4 inches may not reach the eyelets or may bind when the spool rotates, preventing line from feeding.

Inserting Line into Eyelets and Reinstalling the Spool

Locating and Understanding Eyelets

Eyelets are small holes or slots on the trimmer head where the line exits and makes contact with the cutting surface. Most trimmers have two eyelets positioned opposite each other (90–180 degrees apart on the head). Line is routed through both eyelets to ensure balanced cutting.

Threading the Line

  1. With the spool wound and the 4–6 inches of free line ready, position the spool so the free line ends face the eyelets.
  2. Insert one free end into one eyelet, pushing it through until approximately 2–3 inches protrude on the opposite side of the head.
  3. Insert the other free end into the second eyelet the same way.
  4. The line should sit symmetrically in both eyelets, with equal lengths protruding.

Reinstalling the Spool

For twist-on spools:

  1. Align the spool threads with the trimmer head threads. Ensure any washers or spacers are positioned correctly underneath the spool (refer to the configuration you noted during removal).
  2. Thread the spool clockwise by hand. Do not force it; it should turn smoothly.
  3. Once hand-tight, use a wrench to tighten an additional quarter-turn. Do not over-tighten, as this can strip the threads or make future removal difficult.

For bump-feed spools:

  1. Align the cartridge so the release tabs match the slots on the trimmer head.
  2. Press the cartridge firmly into the head. You should hear or feel a click as the tabs lock into place.
  3. Verify that both tabs are fully seated and the cartridge does not wiggle or move.

Testing Line Feed

Before using the trimmer, test the line to ensure it feeds properly:

  1. Reconnect the spark plug wire (gas) or battery (electric).
  2. Hold the trimmer firmly and rotate the cutting head by hand (do not start the engine yet). The line should unwind gradually and smoothly.
  3. If the line binds, stops, or wraps around the spool, stop and recheck the winding direction and spool alignment.
  4. Once hand-rotation feels smooth, start the trimmer at low speed and listen for binding or unusual noise. The line should advance without resistance.

Common Installation Mistakes and Troubleshooting

Line Won’t Feed or Advances Unevenly

Possible causes: Line wound in wrong direction, spool not fully seated, or line tangled on the spool hub.

Solution: Remove the spool and verify the winding direction matches the arrow markings. Check that no line is wrapped around the hub. Reinstall the spool and test again.

Line Jams or Binds During Operation

Possible causes: Too much free line, line wound too loosely, or incorrect line gauge.

Solution: Reduce the free line length to 4–5 inches if you left more than 6. Rewind the spool with tighter tension. Confirm you are using the correct gauge by checking your manual.

Line Tangles or Wraps Around Spool

Possible causes: Line overlapped during winding, spool off-center, or line not seated in the starting notch.

Solution: Unwind and rewind the line, ensuring each pass overlaps slightly without creating gaps or bunches. Verify the starting notch is secure.

Line Cuts Unevenly or Stops Cutting

Possible causes: One line end is longer than the other, or eyelet is damaged or clogged.

Solution: Trim both line ends to equal length (typically 4–6 inches protruding from each eyelet). Inspect the eyelet for cracks, blockages, or rough edges; file smooth if necessary.

Spool Difficult to Remove

Possible causes: Previous over-tightening, corrosion, or thread damage.

Solution: Apply penetrating oil (WD-40 or similar) around the spool threads and let it sit for 15 minutes. Use a wrench for better leverage and rotate gently. If the spool still resists, do not force; contact the manufacturer or a repair shop to avoid damaging the trimmer head.

Frequently Asked Questions

How often should I replace trimmer line?

Line replacement frequency depends on usage. Residential users typically replace line every 2–4 weeks of regular mowing season use. Commercial or heavy-use operators may replace line weekly or even during a single day of heavy work. Replace line whenever it becomes too short to cut effectively or when it breaks during operation.

Can I use a different line gauge than what the manual specifies?

No. Using a gauge different from the manufacturer’s specification can damage the trimmer’s gearbox, cause line to jam, or create unbalanced cutting. Always use the exact gauge listed in your manual. If your manual is unavailable, contact the manufacturer or consult the trimmer head label.

Why does my line keep breaking?

Line breaks due to hitting hard objects (rocks, concrete), improper winding (too loose or wrong direction), incorrect gauge, or old, brittle line. Inspect the cutting area for debris, verify your winding technique, and ensure you are using fresh line. Very old line becomes brittle and breaks easily even during normal use.

Do I need special tools to replace trimmer line?

Most twist-on spools require only your hands or a basic wrench. Bump-feed systems may require a flathead screwdriver to press release tabs. No specialized tools are necessary for standard residential trimmers. Check your manual for any specific tools recommended for your model.