How Do You Change Trimmer Line? (Complete Guide for All Head Types)

Direct Answer: How to Change Trimmer Line

To change trimmer line, first identify your trimmer head type—bump feed (most common), fixed spool, or automatic. Stop the trimmer and unplug it if electric. For bump feed heads: remove the spool, wind new line around it in the correct direction (usually counterclockwise), thread the ends into guide slots, and reinstall. For fixed spool heads: remove the cover, manually wind line onto the fixed spool, and secure the ends. For automatic heads: simply insert new line into the cartridge opening and let the mechanism feed it as needed. Always use the correct line gauge (typically 0.065″ to 0.110″) specified for your trimmer model.

Identify Your Trimmer Head Type

Before you start, knowing your trimmer head design is essential—replacement procedures differ significantly between the three main types.

Bump Feed Head (Most Common)

This is the standard design on most residential trimmers. The spool sits inside a removable head cover and “bumps” the ground to release more line as it wears. When you tap the head on the ground, a spring mechanism advances fresh line. The spool is easily removable, making this design the most user-friendly for line replacement.

Fixed Spool Head

Less common on modern trimmers but still found on some professional and older models, the fixed spool head has the line wound directly onto a stationary spool inside the head. There’s no removable spool cartridge, so you wind line manually onto the spool in place, usually accessing it by removing a cover plate.

Automatic Feed Head

Premium trimmers often feature automatic feed heads that sense line wear and advance new line without bumping. You simply insert line into a cartridge or opening, and the mechanism handles the rest. These require the least manual intervention but may cost more to replace when needed.

To find your head type: Check your trimmer’s manual or manufacturer’s website. You can also search online for “[your trimmer model] head type” to see product images. Gas, electric, and cordless trimmers all use these same head designs—the power source doesn’t affect the head mechanism.

Safety Precautions Before Starting

• Stop the trimmer completely. Never attempt line replacement while the trimmer is running.
• Unplug electric trimmers or remove the battery from cordless models. This prevents accidental activation.
• Allow gas-powered trimmers to cool for 5-10 minutes after use before handling the head.
• Wear cut-resistant gloves when handling trimmer line, especially broken or coiled line.
• Work on a clean, flat surface to avoid losing small parts (springs, guides, or spool components).
• Keep the trimmer head pointed away from your body while working on it.

Tools and Materials You’ll Need

Tools

• Socket wrench or hex key (size varies by model; check your manual)
• Screwdriver (flathead or Phillips, depending on your trimmer)
• Small pliers (helpful for managing springs or stubborn spool removal)
• Work gloves (cut-resistant preferred)
• Container or small bag (to hold removed parts)

Materials

• Replacement trimmer line in the correct gauge for your model

Selecting the Right Trimmer Line

Trimmer line comes in different gauges (thicknesses) and materials. Choosing the wrong gauge can cause the trimmer to malfunction.

How to find your line gauge: Check the trimmer’s user manual, the specifications label on the trimmer head, or the manufacturer’s website. Using a gauge that’s too thick can strain the motor and increase line breakage. Too thin, and the line snaps easily. When in doubt, use the gauge specified in your manual.

Line material options: Most residential line is round nylon. Some trimmers use twisted or square-shaped line for added durability, but always match the profile your trimmer was designed for.

Step-by-Step: Replacing Line on a Bump Feed Head

This is the most common trimmer head design and the easiest to service.

Step 1: Remove the Spool

1. Locate the fastener (usually a socket bolt or hex nut) at the center of the trimmer head.
2. Use the appropriate wrench or hex key to loosen and remove the bolt.
3. Gently lift the spool out of the head housing. A spring may be attached—keep track of its position for reinstallation.
4. If line remains on the spool, discard it or save it as scrap.

Step 2: Wind New Line onto the Spool

1. Most spools have two guide slots or notches indicating the winding direction. Check your manual—usually counterclockwise when viewed from above.
2. Insert one end of the new trimmer line into the notch and wind it tightly around the spool, keeping tension consistent.
3. Wind until you’ve used the recommended length—typically 15-20 feet, though this varies by spool size. Your manual will specify.
4. Leave approximately 6-8 inches of line unwound at the end.

Step 3: Thread the Line into Guide Slots

1. Most spool designs have two notches on opposite sides of the spool rim.
2. Pull the wound line tight and thread each end into the outer guide notches, leaving 4-6 inches of line extending beyond the spool.
3. Ensure the line sits securely in the notches—it should not slip out when you tug gently.

Step 4: Reinstall the Spool

1. Lower the spool back into the head housing, aligning the center hole with the bolt hole.
2. If there’s a spring, ensure it’s positioned correctly (usually sits on top of the spool center).
3. Replace the bolt and tighten securely with your wrench or hex key. Do not overtighten—snug is sufficient.

Step 5: Test the Bump Feed

1. Plug in or turn on the trimmer (in a safe area, away from people and obstacles).
2. Run the trimmer briefly at low speed to check that line feeds smoothly.
3. Tap the trimmer head gently on the ground to test the bump feed mechanism—fresh line should advance.
4. If line doesn’t advance or tangles, stop and adjust the winding or line positioning.

Step-by-Step: Replacing Line on a Fixed Spool Head

This older design requires manual winding directly onto a stationary spool inside the head.

Step 1: Remove the Head Cover

1. Locate the cover plate or access panel (usually held by 1-2 screws).
2. Remove screws and carefully lift the cover to expose the fixed spool.
3. Note the position of any springs or guides—take a photo if helpful for reassembly.

Step 2: Clear Old Line

1. Remove all remaining old line from the spool, including any wrapped around the arbor (center post).
2. Inspect the spool for cracks or damage. If damaged, contact the manufacturer for a replacement spool.

Step 3: Wind New Line

1. Locate the direction indicator or arrow on the spool showing winding direction.
2. Starting at the arbor (center), wind new line tightly, wrapping the spool in the indicated direction.
3. Keep tension consistent to avoid loose or bunched line.
4. Wind until the spool is full or until you’ve reached the recommended line length for your model.

Step 4: Secure the Line Ends

1. Leave 6-8 inches of line unwound.
2. Thread each end through the exit guides or slots on the spool (usually two slots on opposite sides).
3. Wrap the ends around the spool perimeter to secure them, or knot them to prevent unraveling.
4. Trim excess line close to the knot.

Step 5: Reinstall the Cover

1. Carefully position the cover back onto the spool, aligning any guides or springs.
2. Replace and tighten screws firmly but not excessively.

Step-by-Step: Replacing Line on an Automatic Feed Head

Automatic heads are the simplest to service—no winding required.

Step 1: Locate the Cartridge Opening

1. Find the line insertion port or cartridge opening on the trimmer head (usually a small hole or slot marked with an arrow or label).
2. Consult your manual if you’re unsure of the exact location.

Step 2: Insert New Line

1. Feed the new trimmer line into the opening, following the direction indicated by any arrows or markings.
2. Push the line in until you feel resistance or hear a click, indicating it’s seated in the feed mechanism.
3. For some models, you may need to insert line into two separate ports (for dual-line heads).

Step 3: Prime the Mechanism (If Needed)

1. Some automatic heads require a “prime” step—lightly tapping the trimmer head on the ground once or twice to activate the feed mechanism.
2. Check your manual for specific priming instructions.

Step 4: Test the Feed

1. Run the trimmer briefly at low speed to verify that line is feeding correctly.
2. If line doesn’t feed or appears stuck, stop immediately and reinsert it, ensuring it’s fully seated.

Common Mistakes and Troubleshooting

Line Keeps Breaking

Causes: Line gauge too thin, incorrect winding direction, line wound too loosely, or hitting hard objects frequently.

Solutions: Check that you’re using the correct gauge for your model. Rewind line tightly and in the correct direction (consult your manual). If you’re hitting rocks or concrete frequently, upgrading to a thicker gauge (if your trimmer allows) can help.

Line Won’t Advance or Feed

Causes: Line wound too tightly, incorrect winding direction, line not seated in guide slots, or a faulty bump feed mechanism.

Solutions: Remove the spool and rewind, ensuring line is tight but not bunched. Verify the winding direction matches your manual. For automatic heads, try reinserting the line and tapping the head on the ground to prime the mechanism. If the problem persists, the head may need replacement.

Trimmer Head Vibrates Excessively

Causes: Uneven line lengths, line not seated evenly in guide slots, or spool not centered properly.

Solutions: Ensure both line ends extending from the spool are approximately equal length. Recheck that the spool is centered and the bolt is tightened evenly. For bump feed heads, verify the spring is positioned correctly.

Line Tangles Inside the Head

Causes: Line wound in the wrong direction, line wound too loosely, or a damaged spool or head housing.

Solutions: Rewind following your manual’s direction carefully. If tangling persists, remove the spool and inspect for cracks or warping. Clean any debris from inside the head housing that could catch line.

How Often Should You Change Trimmer Line?

Line replacement frequency depends on usage:

• Residential use (weekly mowing): Change line every 3-4 weeks during mowing season.
• Heavy use or commercial applications: Every 1-2 weeks.
• Occasional use: Every 6-8 weeks.
• Signs it’s time to change: Visible wear or fraying, frequent line breakage, or noticeably reduced cutting performance.

Many users find it convenient to wind a new spool at the start of each season to avoid mid-season hassles.

Frequently Asked Questions

Can I use any trimmer line on my trimmer?

No. Trimmer line gauge must match your trimmer’s specifications. Using the wrong gauge can damage the trimmer, cause excessive line breakage, or prevent proper feeding. Always check your manual or the manufacturer’s website for the correct gauge. When replacing line, buy the exact gauge your trimmer requires—usually printed on the trimmer head or in the user manual.

How much trimmer line do I need?

A typical residential spool holds 15-20 feet of line, though this varies by model. Your trimmer’s manual will specify the recommended line length for your spool. Most stores sell trimmer line in bulk (usually 50-100 feet per spool), so one package will last through multiple refills. Automatic feed heads may specify different line lengths—consult your manual.

What’s the difference between round and twisted trimmer line?

Round line is the most common and works well for general grass and light weeds. Twisted or square-shaped line is slightly more durable and cuts better through thicker weeds or brush. However, you must use the profile your trimmer was designed for—installing twisted line in a trimmer designed for round line (or vice versa) can cause feeding problems. Stick with the profile specified in your manual.

Why does my new line break so easily?

Common causes include using too thin a gauge for your trimmer, winding line too loosely (so it doesn’t have structural support), hitting rocks or concrete frequently, or hitting hard objects at high speed. If you’re using the correct gauge and winding tightly, the issue may be your cutting environment. Consider upgrading to a heavier gauge if your trimmer allows it, or avoid hitting solid objects when possible.

When to Replace vs. Repair the Trimmer Head

If you’re having persistent problems after multiple attempts to correctly wind or install line, the issue may be with the head itself, not the line or your technique.

Signs you need a new head:

• Cracks or visible damage to the spool or housing
• The bump feed mechanism no longer advances line even after proper installation
• Excessive vibration that doesn’t resolve after rewinding
• Line constantly tangles regardless of winding direction or technique

Replacement heads are available for most popular trimmers. Check your trimmer’s model number and search for “[model] replacement head” online or contact the manufacturer. Professional repair shops can also diagnose head issues if you’re unsure whether replacement is necessary.