How Do You Restring a Grass Trimmer? (Step-by-Step Guide)

Quick Answer: How to Restring a Grass Trimmer

To restring a grass trimmer, remove the spool from the trimmer head, extract the old line, measure and cut new line (typically 15–25 feet per spool, depending on head capacity), wind it onto the spool in the correct direction (usually counterclockwise when viewed from above), thread the ends through the eyelets, and reinstall the spool. The exact process depends on your trimmer’s head type—bump-feed heads tap the ground to advance line, while fixed-spool heads require manual line advancement. Most trimmers use 0.065 to 0.085-inch diameter nylon line.

Understanding Your Trimmer Head Type

Before restringing, identify which head design your trimmer uses. This determines how you wind the line and how it advances during operation.

Bump-Feed Trimmer Heads

Bump-feed heads are the most common and user-friendly design. They feature a spring-loaded spool that automatically feeds line as you tap the head on the ground during use. When you tap the trimmer head against the ground, a spring mechanism releases just enough line to replace the worn portion. This design is popular on consumer and mid-range trimmers because it requires minimal maintenance during operation.

Advantages: Automatic line advancement, simple to operate, reduced downtime during use.

Disadvantages: Spring mechanisms can wear out over time; tapping the ground must be done correctly to trigger line feed.

Fixed-Spool Trimmer Heads

Fixed-spool heads have a stationary spool with line that you manually advance by turning a knob or collar on the head. You must stop the trimmer and manually feed out line when it wears down. These heads are common on commercial-grade and professional trimmers.

Advantages: Durable, predictable line advancement, no springs to wear out.

Disadvantages: Requires manual intervention; more downtime during trimming jobs.

How to Identify Your Head Type

• Look at the trimmer head exterior. Bump-feed heads usually have a plastic cap on top with a spring mechanism visible when you remove it.
• Check your trimmer’s manual for head type classification.
• If the head has a rotating knob or collar at the base that you turn to advance line, it’s a fixed-spool design.
• If tapping the head on the ground releases line during operation, you have a bump-feed head.

Selecting the Correct Trimmer Line

Choosing the right line is critical for proper trimmer performance and safety. Using incorrect line diameter can cause the trimmer to jam, overheat, or perform poorly.

Understanding Line Gauge (Diameter)

Trimmer line is measured in inches, with most consumer trimmers using one of three standard gauges:

To find your trimmer’s required line gauge, check the user manual, look for markings on the trimmer head itself, or consult the manufacturer’s website using your trimmer model number. Using line that’s too thin may cause frequent breakage; line that’s too thick can overload the motor and cause jamming.

Line Materials and Options

Nylon (most common): Standard nylon line is affordable, widely available, and suitable for most residential trimming. It degrades slightly from UV exposure over time.

Co-polymer nylon: Enhanced nylon blends offer improved durability and longer lifespan, reducing replacement frequency.

Reinforced nylon: Some lines contain additives or reinforcement for extra toughness. These are more expensive but last longer in commercial or heavy-use settings.

For most residential users, standard nylon line is sufficient and cost-effective.

Calculating Line Length Needed

Most trimmer spools require 15–25 feet of line, depending on spool diameter and design. To determine your spool capacity:

• Check your trimmer’s manual for exact line length specifications.
• Look for markings on the spool itself indicating line capacity.
• When in doubt, pre-wound replacement spools for your model include the correct amount.

If you’re buying bulk line, it’s often sold in 100-foot or longer packages. Buying bulk is economical if you trim frequently or maintain multiple trimmers.

Removing the Old Line and Spool

Before removing the spool, ensure the trimmer is off and cool, and disconnect the spark plug wire (for gas trimmers) or remove the battery (for cordless models) to prevent accidental startup.

Step 1: Access the Spool

• Locate the trimmer head cap (usually a plastic cover on top of the head).
• For bump-feed heads, the cap typically unthreads counterclockwise or has clips/tabs you press to release it.
• For fixed-spool heads, you may need to remove a retaining bolt or collar.
• Consult your manual if you’re unsure how your specific head disassembles.

Step 2: Remove the Spool

• After the cap is removed, the spool should lift out or unscrew from the trimmer shaft.
• If the spool is stuck, gently work it side-to-side; do not force it, as you may strip the threads.
• Set the spool on a clean work surface.

Step 3: Extract Old Line

• Pull away any remaining line from the spool. Most of it should come free easily.
• If line is wound tightly or hardened, gently pick at the starting end with your fingernail or a small tool to loosen it.
• Once loosened, the line should unwind smoothly.
• Dispose of the old line appropriately (it’s not recyclable in most programs).

Step 4: Clean the Spool (Optional but Recommended)

• Wipe the spool clean with a dry cloth to remove grass debris or dirt.
• Inspect it for cracks or damage. If the spool is cracked, it should be replaced before restringing.
• Check that the spool rotates freely on its center post.

Winding New Line on the Spool

Proper winding is essential for smooth line feed and reliable operation. The process differs slightly for single-line and dual-line configurations.

General Winding Principles

• Direction matters: Most bump-feed spools wind counterclockwise when viewed from above; check your manual or markings on the spool for directional arrows.
• Wind tightly: The line should be wound in neat, evenly spaced layers to prevent tangling and ensure even line feed.
• Tension: Maintain moderate tension as you wind so the line doesn’t bunch or overlap.
• Fill the spool: Wind until you reach near the edge of the spool, leaving just enough space that the line doesn’t spill out.

Winding a Single-Line Spool

1. Cut your line to the specified length (typically 15–25 feet). Make both ends as square as possible with a sharp utility knife or line cutter for easier threading.
2. Locate the line anchor slot or hole on the spool. This is usually a small notch or hole near the center.
3. Insert one end of the line into the anchor slot and hold it firmly in place with your thumb and finger.
4. Begin winding the line onto the spool in the correct direction (counterclockwise for most bump-feed heads), maintaining even tension.
5. Wind layer by layer, keeping the line neatly aligned and not overlapping.
6. Continue winding until the desired amount is on the spool, leaving about 4–6 inches of line free.
7. Once wound, the free end should exit near the edge of the spool. Leave this end uncut for now.

Winding a Dual-Line Spool

1. Cut two equal lengths of line (usually 15–25 feet each), making sure both pieces are exactly the same length for balanced cutting.
2. Most dual-line spools have a center divider or guide. Position one line on each side of this divider.
3. Find the anchor slots (usually two, one for each line) and insert each line end securely.
4. Wind both lines simultaneously, maintaining equal tension on each. The lines should wind in opposite directions on either side of the divider (e.g., line 1 winds counterclockwise, line 2 winds clockwise).
5. Keep both sides balanced—if one side has more line than the other, the trimmer head will vibrate and produce uneven cuts.
6. Wind until both sides reach the edge of the spool, with about 4–6 inches of each line free.
7. Double-check that both free ends are approximately the same length before reinstalling.

Preventing Tangling and Jamming

• Ensure the line doesn’t cross over itself during winding, as this causes tangling when the spool rotates.
• Don’t wind too loosely; slack line can shift inside the head and jam.
• Don’t wind too tightly; excessive tension can cause the spool to bind and prevent line feed.
• Verify the line exits the anchor slot cleanly and doesn’t wrap back over the wound line.

Reinstalling the Spool and Threading the Line

Proper reinstallation ensures the trimmer operates smoothly and the line advances correctly.

Step 1: Thread the Line Through Eyelets

• Most trimmer heads have one or two small eyelets (holes or guides) near the edge of the head where the line exits and cuts.
• Gently pull the free end(s) of line through the eyelet(s), starting from the inside of the head and exiting outward.
• For dual-line spools, thread one line through each eyelet, ensuring neither line is twisted or kinked.
• Pull each line taut so it sits evenly in its eyelet.

Step 2: Reattach the Spool to the Shaft

• Lower the spool back onto the trimmer shaft, aligning the center hole with the shaft.
• If the spool screws onto the shaft, rotate it clockwise until hand-tight. Do not over-tighten, as this can strip the threads.
• For bump-feed heads, ensure the spool spins freely and isn’t binding.

Step 3: Reattach the Head Cap

• Place the head cap back onto the trimmer head, aligning any tabs or markings.
• Screw it clockwise or secure it with clips until snug. Again, avoid over-tightening.
• Verify the cap is fully seated and doesn’t wobble.

Step 4: Trim Excess Line

• Cut the free ends of line to the correct cutting length. Most trimmers cut most effectively with line extending 4–6 inches beyond the trimmer head.
• Use a utility knife or line cutter for clean, straight cuts.
• Ensure both lines (if dual-line) are exactly the same length for balanced cutting.

Testing the Trimmer After Restringing

Before using the trimmer on your lawn, perform a quick safety and functionality check:

1. Reconnect power: Reattach the spark plug wire (gas) or battery (cordless), or plug in the trimmer (electric).
2. Start the trimmer: Turn it on and let it run for 10–15 seconds at idle to ensure the motor starts smoothly.
3. Listen for unusual sounds: Grinding, rattling, or squealing may indicate the line is jammed or improperly wound. Stop immediately and troubleshoot.
4. Observe line feed: For bump-feed heads, tap the head gently on the ground once or twice. You should hear or feel the line advance slightly. For fixed-spool heads, manually advance the line a quarter turn and observe that new line emerges.
5. Test cutting: Run the trimmer over a small patch of grass and check that it cuts cleanly and smoothly without vibration.
6. Check line length: After a minute of use, inspect the line for wear. It should wear evenly from both ends (if dual-line) and gradually shorten as you trim.

If everything looks good, your trimmer is ready for regular use.

Troubleshooting Common Restringing Problems

Line Won’t Advance (Bump-Feed Heads)

Cause: The spring mechanism is stuck or the line is binding in the anchor slot.

Solution: Remove the head cap and inspect the spring. Clean any debris and apply a light lubricant if needed. Ensure the line is properly seated in the anchor slot and isn’t wrapped under itself. If the spring is damaged, the head may need replacement.

Line Tangles or Jams Inside the Head

Cause: The line was wound too loosely, crossed over itself during winding, or is improperly threaded through the eyelets.

Solution: Remove the head cap and spool. Unwind the line completely and rewind it more tightly, ensuring it doesn’t overlap itself. Verify the line exits cleanly from the anchor slot and threads straight through the eyelet without kinks.

Uneven Line Length on Dual-Line Trimmer

Cause: The lines were wound with unequal tension or the spool was filled unevenly.

Solution: Remove the spool and rewind both lines simultaneously, maintaining equal tension. Verify both lines extend the same distance from the spool edges before reinstalling. If one line wears faster than the other during use, it may indicate the spool or head is warped.

Line Keeps Breaking Frequently

Cause: The line is too thin for your trimmer, the cutting head has rough edges that fray the line, or the line is winding incorrectly and weakening.

Solution: Verify you’re using the correct line gauge for your trimmer model. Inspect the eyelets and cutting head for rough edges or burrs; smooth these with fine sandpaper if needed. Ensure the line is wound tightly and evenly.

Motor Sounds Strained or Overheating

Cause: The line diameter is too large, the spool is over-filled and creating drag, or the line is binding in the head.

Solution: Confirm you’re using the correct line gauge. Check that the spool cap closes fully without resistance. Remove the head and manually spin the spool—it should rotate freely with minimal drag. If it doesn’t, rewind the line.

Frequently Asked Questions

How often should I restring my grass trimmer?

This depends on trimming frequency and grass type. Residential users who trim once a week might restring every 2–4 weeks during the growing season. Heavy commercial use may require restringing every few days. You’ll know it’s time when the line becomes visibly short (less than 2 inches) or stops cutting effectively.

Can I use any brand of trimmer line on my trimmer?

Yes, as long as the line diameter matches your trimmer’s specifications. You don’t need to buy the exact brand your trimmer manufacturer recommends—any 0.065, 0.080, or 0.085-inch nylon line (depending on your trimmer’s requirement) will work. Generic lines are often cheaper than branded replacements.

What if my trimmer uses a pre-wound spool cartridge instead of manual winding?

Some trimmers, especially commercial models, use disposable pre-wound cartridge spools. For these, simply unscrew the old cartridge from the head and screw in a new one. No winding is needed. These cartridges are more expensive per use but save time and ensure consistent winding.

Can I mix different line gauges in a dual-line trimmer?

No. Both lines must be the same gauge. Mismatched lines create imbalanced cutting, vibration, and uneven wear. Always use identical line sizes for both sides of a dual-line spool.

Why does my trimmer line keep tying itself in knots inside the head?

This usually indicates loose winding or improper anchor placement. Rewind the line more tightly, ensuring each layer sits neatly on top of the previous one without gaps. Verify the anchor slot is holding the starting end securely. If the problem persists, the spool may be warped and need replacement.