How to Replace a Trimmer Head on a Weed Eater

The trimmer head is the business end of your weed eater — it holds the line that does the cutting. Over time, the head wears out, jams, or breaks, making trimming frustrating and inefficient. Replacing the trimmer head is a quick job that takes 10–15 minutes and can dramatically improve your trimming experience.

Signs You Need a New Trimmer Head

• The line won't feed (bump feed mechanism is worn)
• The head is cracked or broken
• The line tangles constantly inside the head
• The head wobbles or spins loosely on the shaft
• You want to switch from bump feed to auto-feed or a fixed-line head

Types of Trimmer Heads

1. Bump Feed Heads

The most common type. You tap the head on the ground to release more line. They're reliable but wear out from the tapping. Most factory heads are bump feed.

2. Auto-Feed Heads

These release line automatically as needed without tapping. They're convenient but can be finicky and may overfeed.

3. Fixed-Line Heads

These hold pre-cut lengths of line instead of a spool. You thread two or four pieces of line through the head. They're the most reliable for heavy use and commercial applications — no tangles, no feeding issues.

4. Blade Heads

Some trimmers accept plastic or metal blades instead of line. These are for heavy brush cutting, not trimming. Check that your trimmer is rated for blade use — using a blade on a trimmer not designed for it is dangerous.

Choosing a Replacement Head

Check the shaft diameter of your trimmer (typically 7/16" or 10mm) and the thread direction (most are left-hand thread, meaning you turn clockwise to remove). Universal heads fit most trimmers, but verify compatibility before buying.

Consider your trimming style:

• Light residential trimming: Bump feed or auto-feed
• Heavy residential or light commercial: Fixed-line head
• Commercial use: Fixed-line or heavy-duty bump feed

Tools You'll Need

• Replacement trimmer head
• Adjustable wrench or the correct socket
• Screwdriver (for some heads)
• Work gloves
• Spark plug wrench (to remove the spark plug for easier shaft turning)

Step 1: Safety First

• Remove the spark plug wire to prevent accidental starting
• Wear gloves — the old line can be sharp and the head may have burrs
• Work on a flat surface

Step 2: Remove the Old Trimmer Head

For Most Trimmers:

1. Lock the shaft — insert a small screwdriver or the trimmer's shaft lock tool into the hole in the shaft housing to prevent the shaft from turning. Some trimmers have a button on the housing you press to lock the shaft.

2. Turn the head clockwise — most trimmer heads are left-hand thread, so you turn clockwise to loosen (opposite of normal). If it won't turn, try the other direction — some are right-hand thread.

3. Remove the head — once loose, unscrew it by hand and remove it from the shaft.

If the Head Is Stuck:

If the head won't unscrew:

• Spray penetrating oil on the threads and wait 10 minutes
• Use a strap wrench to grip the head without damaging it
• Tap the wrench handle gently with a mallet to break the thread loose
• If the head is damaged beyond use, you can cut it off with a hacksaw — but be careful not to damage the shaft threads

For Heads with a Center Bolt:

Some heads (particularly on straight-shaft trimmers) are held by a center bolt:

1. Lock the shaft
2. Remove the center bolt with the correct socket (usually 10mm or 12mm)
3. Lift off the head and any spacers

Step 3: Clean the Shaft

Clean the threads on the shaft with a wire brush. Check for damage or burrs that could prevent the new head from threading on smoothly. Apply a small amount of anti-seize compound to the threads — this makes future removal easier.

Step 4: Install the New Head

For Screw-On Heads:

1. Thread the new head onto the shaft (counter-clockwise for left-hand thread)
2. Hand-tighten until snug
3. Lock the shaft and tighten an additional 1/4 turn with a wrench — do not over-tighten

For Bolt-On Heads:

1. Place any spacers on the shaft in the correct order
2. Position the head on the shaft
3. Install and tighten the center bolt

Step 5: Load the Line (For Spool Heads)

If your new head uses a spool:

1. Cut the correct length of trimmer line (check the manual for diameter and length)
2. Insert one end into the anchor hole on the spool
3. Wind the line in the direction indicated by the arrow on the spool — winding the wrong way prevents feeding
4. Leave 5–6 inches of line extending from the head
5. Thread the line through the eyelets in the head
6. Snap the spool into the head

For fixed-line heads, cut two or four pieces of line to the specified length and thread them through the head per the instructions.

Step 6: Test

1. Reconnect the spark plug wire
2. Start the trimmer and let it run for 30 seconds
3. Check that the head spins true without wobble
4. If you have a bump feed head, tap it on the ground (while running at full throttle) to test the feed mechanism
5. Check for excessive vibration — a loose or unbalanced head vibrates badly. Stop and re-tighten if needed.

Maintenance Tips

• Clean the head after each use — grass and debris build up inside and jam the feed mechanism
• Replace the line before it's completely gone — running with no line damages the head
• Use the correct line diameter — too thick jams the head; too thin breaks too easily
• Store the trimmer with the head off the ground — resting on the head deforms the feed mechanism
• Keep a spare pre-wound spool — swapping spools is faster than re-winding in the field

The Bottom Line

A new trimmer head costs $15–40 and takes 15 minutes to install. If your current head is jammed, cracked, or frustrating to use, replace it — you'll save time and aggravation on every trimming job. For most homeowners, a fixed-line head is the most reliable upgrade from a worn-out factory bump feed head.