How to Fit Trimmer Line? (The Quick Answer)
Fitting new trimmer line, also called weed eater or string trimmer line, takes about 10 minutes and requires no special skills. The exact method depends on your trimmer head type, but every approach follows the same core steps: disconnect the power, open the head, remove old line, load fresh line, and reassemble so that roughly 4 to 6 inches (10 to 15 cm) of line extends from the head.
- Disconnect the trimmer (unplug it, remove the battery, or pull the spark plug wire).
- Identify your head type: bump feed, fixed line, or auto feed.
- Use the correct line diameter listed in your manual (most home trimmers accept 0.065 to 0.095 inch).
- Load the line exactly as described below for your head type to prevent tangles and jams.
Understanding Your Trimmer Head Type
Before you touch a single strand of line, look at the head on the bottom of your trimmer. The three main designs load differently, and using the wrong method is the number one cause of tangled, jammed, or ineffective line.
Bump Feed Heads
The most common design on home trimmers. You feed the line by tapping or bumping the head gently on the ground while the trimmer is running. The spool releases a small amount of line each time you bump, so you never have to stop and extend the line by hand. Fitting line on a bump feed head means removing the spool, winding a long continuous length of line onto it, and threading the two ends through the eyelets.
Fixed Line Heads
Often called snap-in or drop-in heads. These use several pre-cut pieces of line rather than a single long spool. There is no bump mechanism, which means fewer moving parts and very few jams, but you must replace all the line pieces by hand when they wear down. Fitting line is a matter of cutting equal lengths and snapping them into the slots or through the eyelets.
Auto-Feed Heads
These feed line automatically using centrifugal force as the head spins, so you do not bump anything. Many auto-feed designs use a pre-wound replacement spool that simply snaps into the head. If you wind the line yourself, follow the technique for bump feed heads, because the internal spool mechanics are similar.
| Head Type | How It Works | Best For |
|---|---|---|
| Bump feed | Tap the head on the ground to release more line | General home trimming; no manual stops needed |
| Fixed line | Pre-cut pieces that must be replaced by hand | Beginners; simple, reliable, few jams |
| Auto feed | Centrifugal force advances line automatically | Users who want zero bumping effort |
Safety and Preparation
Before you open the head, take a few minutes to prepare. Working safely is just as important as winding a neat spool.
What You Will Need
- New trimmer line in the correct diameter for your model
- Work gloves to protect your hands from old line and sharp nylon
- A clean, flat work surface
- A small flat-head screwdriver for heads held by clips or tabs (if needed)
- A rag or brush to clean grass and debris out of the head
Safety Steps
- Disconnect the power source completely: unplug an electric trimmer, remove the battery from a cordless model, or disconnect the spark plug wire on a gas trimmer.
- Wait for the cutting head to stop completely before touching it. The line can keep the head spinning briefly after shutdown.
- Wear safety glasses and work gloves. Old line can hold grit and sharp pieces of grass, and putting the spool back together can pinch fingers.
- Work on a clean surface so small parts like springs, washers, and caps do not roll away.
Check your owner’s manual for the recommended line diameter. Using a line that is too thick will jam the feed mechanism, while a too-thin line will break constantly and cut poorly.
Step-by-Step Guide for Bump Feed Heads
These steps work for the vast majority of bump feed string trimmers. If your manual shows a slightly different spool arrangement, follow the manual but keep the same principles: clean, even winding with no crossed strands.
Step 1: Open the Head and Remove Old Line
Hold the head and look for the release tabs or an arrow near the cap. Press the tabs on the sides of the head (or push the cap down and turn it) to release the spool. Lift the spool out and remove every scrap of old line, including any tangled pieces stuck in the eyelets. Clean grass, dirt, and oil from the spool and the inside of the head with a rag.
Step 2: Measure and Cut the Line
Most bump feed spools hold one continuous length of line that works on both sides of the head. A standard full spool takes about 15 to 25 feet (4.5 to 7.5 m) of line in total. Cut a single piece and fold it in half so both ends are equal. If you are not sure how much your spool holds, start with a conservative 15 feet and add more if the spool still has room.
Step 3: Wind the Line onto the Spool
Locate the slot or notch in the middle of the spool. Hook the center of your folded line into the slot. Now wind the two halves onto the spool in the direction shown by the arrow printed on the spool (usually the same direction the head rotates). Keep the line taut but relaxed enough that it does not stretch, wind it in neat, even rows, one half on top of the other, and never let the strands cross. Stop when the line is level with the edge of the spool so it can still spin freely inside the head.
Step 4: Hook the Ends and Thread the Eyelets
When the spool is full, tuck each loose end into the small retaining notches on the rim of the spool. Slide the spool back into the head, aligning the two ends with the eyelets (the small holes on the outside of the head). Push each line end through its eyelet until it appears on the outside. Hold the spool in place and pull both ends firmly to seat it, then replace the cap until it clicks.
Step 5: Test and Adjust the Cutting Length
Pull both lines so they extend 4 to 6 inches from the head. Reconnect the power, hold the trimmer away from your body, and run it at full speed. Tap the head gently on the ground if you need a little more line. The head should feed smoothly and the line should stay put during normal trimming.
Step-by-Step Guide for Fixed Line Heads
Fixed line heads are simpler to service because there is no spool to wind. The job is just cutting equal pieces and seating them properly.
Step 1: Open the Head
Remove the old line pieces. Most fixed heads either turn to open, have a small latch, or use a ring that snaps open with a flat-head screwdriver. Clean out the openings and remove debris so the new pieces seat fully.
Step 2: Measure and Cut the Pieces
Each fixed head usually takes two, three, or four pieces of line. Cut every piece the same length so the head stays balanced (an unbalanced head vibrates heavily). A good starting length is 6 to 8 inches (15 to 20 cm) per piece, slightly longer than the diameter of the head. Check your manual, as some heads specify an exact length.
Step 3: Insert the Line into the Eyelets
Push one end of a piece through the eyelet until it reaches the internal channel. Depending on the design, you either push it in until it locks, or hook it around an internal post and pull it back out the same hole. Insert all pieces in the same orientation.
Step 4: Even the Line and Reassemble
Make sure each piece extends the same distance from the head. Replace any retainer ring or snap the cover back on. Give each line a gentle tug to confirm it is locked in place, then trim the ends with scissors so they are even.
How to Fit Line on an Auto-Feed Head
Auto-feed heads rarely need manual winding because most accept a pre-wound replacement spool. Open the head, remove the old spool, slide the new spool in so the line ends align with the eyelets, and thread the ends through. Pull the line to remove slack before running the trimmer; the first few seconds of spinning will advance the line automatically. If your model is spool-wound rather than cartridge-based, use the bump feed winding instructions above because the internal spool is essentially the same.
Choosing the Right Trimmer Line
Line diameter matters more than any other factor for smooth feeding and good cutting. Using the wrong gauge is a leading cause of jams and premature breakage.
| Line Diameter | Typical Use | Notes |
|---|---|---|
| 0.065 to 0.080 inch | Small electric and battery trimmers, light grass | Thin and light; feeds easily, breaks quickly on rough surfaces |
| 0.085 to 0.095 inch | Standard gas trimmers, medium duty | Most common all-round size for home use |
| 0.105 inch and up | Commercial and heavy-duty trimmers | Very aggressive cutting; requires a powerful head |
Line also comes in shapes: round line cuts quietly and works well for light trimming, twisted or square line cuts faster and lasts longer, and serrated or star line handles thick weeds but wears the head faster. Match the shape to the job, but always match the diameter to your head. When in doubt, a round or lightly twisted 0.080 inch line is the safe choice for most home trimmers.
Common Problems and Troubleshooting
Even careful installs can develop issues. Here is how to fix the most common ones.
The Line Will Not Feed When You Bump
- Too much line on the spool: remove a few feet.
- Line threaded through the wrong eyelets or pulled too tight.
- Debris jammed between the spool and head.
- The bump mechanism, spring, or tab is worn and needs replacing.
The Line Tangles Inside the Head
- Line wound in the wrong direction: rewind following the arrow.
- Line was wound loosely and crossed over itself: rewind in neat rows.
- Line is too thick for the spool: use the diameter in your manual.
The Line Breaks or Wears Out Very Fast
- Line is too thin: upgrade one size if the head allows.
- Trimming against concrete, brick, or fencing shreds line quickly.
- The line is old and dried out: soak it in water for an hour before use.
The Trimmer Vibrates Heavily
On fixed line heads, uneven line lengths cause vibration. Cut all pieces to exactly the same length. On bump feed heads, make sure both strands are pulled out evenly.
Maintenance Tips for Optimal Performance
- Check the line before each session; replace it when it is less than 3 inches from the head.
- Keep the line slightly damp by storing it in a plastic bag or soaking it before use, which prevents brittleness and breakage.
- Clean the head after every few uses, removing grass, oil, and grit that clog the feed mechanism.
- Store the trimmer indoors or under cover in a cool, dry place. Heat and sunlight dry the line and make it snap.
- Use the trimmer at full throttle; running at low speed causes the line to bend, melt, and break.
- Let the trimmer do the work; slicing into soil, rock, or fencing destroys line quickly and can damage the head.
Frequently Asked Questions
How often should I replace my trimmer line?
Replace the line whenever it wears down to about 3 inches of exposed length, or as soon as it shows heavy fraying. In light trimming, one full spool can last several sessions; in tough weeds near hard surfaces, expect to reload more often.
What happens if I use the wrong line diameter?
Line that is too thick jams the feed mechanism and strains the motor, while line that is too thin breaks frequently and cuts poorly. Always check the range printed in your trimmer manual before buying replacement line.
Do I need to remove the battery to change trimmer line?
Yes. For cordless trimmers, remove the battery; for corded models, unplug them; and for gas models, disconnect the spark plug wire. The head can spin without warning if power remains connected, which risks serious injury.
Why does my line keep coming out of the head?
This usually means the line was not seated in the retaining notches, the cap was not clicked fully closed, or the line is too thin for the eyelets so it slides free. Re-open the head, re-seat the ends, and confirm the cap clicks.
