Quick Answer: To replace a string trimmer head, first disconnect the spark plug or battery, then lock the gearcase arbor using a small screwdriver or locking pin through the alignment holes. Unscrew the old head by turning it clockwise (most models use a left-hand reverse thread arbor bolt). Install the new universal speed feed head by threading it counter-clockwise onto the arbor, ensuring the drive tabs engage the gearcase slots, then re-secure the arbor bolt and restring with the appropriate line diameter.
Whether you’re dealing with a stripped bump feed mechanism, a head that won’t advance line, or you simply want to upgrade to a more efficient universal speed feed head, replacing your string trimmer head is a straightforward repair that saves the cost of a new trimmer. This guide covers every trimmer type—from gas-powered to cordless electric—and walks you through the exact process, including how to lock the gearcase arbor, handle left-hand reverse thread arbor bolts, and clear melted trimmer line that has fused inside the head. Standard operational and maintenance protocols can be consulted via EPA Clean Air Act standards for non-road small engines.
Bump Feed vs. Fixed Line Head: Which Type Are You Replacing?
- Socket wrench or Allen key set (typically 24mm, 28mm, or 7/8″ for the arbor bolt)
- Small screwdriver or dedicated arbor locking pin
- Replacement trimmer head (universal speed feed recommended)
- Trimming line in the correct diameter for your trimmer (check owner’s manual)
- Safety glasses and work gloves
- Needle-nose pliers (for removing melted line remnants)
- Penetrating oil (optional, for seized arbor bolts)
Step-by-Step: How to Replace a String Trimmer Head
Step 1: Prepare the Trimmer Safely
Always begin by disconnecting the power source. For gas trimmers, remove the spark plug wire and tuck it away from the plug. For cordless electric trimmers, remove the battery pack entirely. For corded models, unplug the unit from the extension cord. This is not optional—spinning trimmer heads cause serious injuries every year.
Place the trimmer on a flat, stable work surface with the cutting head accessible. If your trimmer has a guard, you can leave it in place for this procedure.
Step 2: Lock the Gearcase Arbor with a Pin or Screwdriver
This is the step most tutorials gloss over, and it’s the reason many people strip their arbor bolt. The gearcase arbor spins freely, so you cannot loosen the head bolt without locking the internal gear in place. Look for a small hole on the side of the gearcase housing, near where the shaft meets the trimmer head. Insert a small screwdriver, hex key, or a dedicated locking pin through this hole until it engages the internal gear and prevents rotation.
Pro tip: On some models, you may need to rotate the head slowly by hand while pressing the pin inward until you feel it drop into the gear slot. Once the pin is seated, the head should not rotate. If you don’t have a locking pin, a 3/32″ or 1/8″ drill bit works as an effective substitute.
Step 3: Remove the Old Trimmer Head (Left-Hand Reverse Thread)
Here is where most people get confused. The arbor bolt on nearly all string trimmers uses a left-hand reverse thread, meaning you turn it clockwise to loosen and counter-clockwise to tighten. This is the opposite of a standard bolt and exists to prevent the spinning head from loosening during operation.
With the arbor locked, place your socket wrench on the arbor bolt and turn it clockwise. It may require significant force, especially if the bolt has never been removed or has accumulated debris. If the bolt is seized, apply penetrating oil around the threads and let it sit for 10–15 minutes before retrying. Once the bolt is loose, continue turning clockwise until the old head detaches from the gearcase.
Step 4: Clear Melted Trimmer Line from the Arbor
If your old head failed because the trimmer line melted and fused inside the spool—a common problem when using low-quality line or operating in heavy grass—you’ll need to clean the arbor area before installing the new head. Melted line typically appears as hardened, discolored plastic residue wrapped around the arbor shaft or caked inside the gearcase opening.
Use needle-nose pliers to pull away any large chunks of melted line. For stubborn residue, a heat gun on low setting (held 4–6 inches away) will soften the plastic enough to scrape it off with a flathead screwdriver. Avoid excessive heat near the gearcase seals. Wipe the arbor threads clean with a rag and a small amount of degreaser before proceeding.
Step 5: Install the New Universal Speed Feed Head
Place the new universal speed feed head onto the arbor, aligning the drive tabs on the head with the corresponding slots on the gearcase. Thread the arbor bolt by hand first, turning it counter-clockwise to engage the left-hand reverse threads. Once hand-tight, use your socket wrench to snug the bolt firmly—do not overtighten, as you can crack the gearcase housing.
Remove the locking pin from the gearcase. Rotate the new head by hand to confirm it spins freely and the drive tabs are properly engaged. If the head wobbles or feels loose, remove it and verify that the drive tabs are seated correctly in the gearcase slots.
Step 6: Restring the New Head
Universal speed feed heads are designed for tool-free restringing. Open the head housing (usually by pressing release tabs or unscrewing the cap), feed the line through the internal channel until equal lengths extend from both eyelets, close the housing, and rotate the bump knob in the direction indicated by the arrow markings to wind the line onto the internal spool. Most speed feed heads accept .065″, .080″, or .095″ line—check your trimmer’s specifications to match the correct diameter.
Reconnect the spark plug wire or battery, and perform a brief test run in an open area to confirm the head spins true and the line advances properly.
Troubleshooting Common Issues After Replacement
Head Won’t Thread Onto the Arbor
If the new head won’t thread onto the arbor, verify you are turning it counter-clockwise (left-hand thread). Also check that the arbor threads are clean and undamaged. Cross-threading is a risk with aluminum arbors—always start by hand before using a wrench.
Line Won’t Advance After Installation
On speed feed heads, ensure the line was wound in the correct direction during restringing. Most heads have internal ratchets that only allow line to advance when wound properly. If the line is wound backwards, open the head and rewind it following the directional arrows.
Excessive Vibration After Head Replacement
Vibration typically indicates an unbalanced head. Ensure equal lengths of line extend from both eyelets. If vibration persists with a new head, the gearcase itself may have worn bearings—a separate repair covered in our gearcase maintenance guide.
Recommended Hardware & Essential Equipment
The following verified replacement heads and line kits are selected for universal compatibility with left-hand reverse thread arbors, durable construction, and tool-free restringing. These specific units solve the most common hardware failures: stripped bump mechanisms, melted line accumulation, and incompatible arbor threads.
Pros
- Fully waterproof and dustproof design means it can handle splashes, spills, and sandy environments.
- Long battery life provides extended playback for camping trips, backyard gatherings, or a full workday.
- Compact and lightweight at 1.21 pounds makes it easy to carry in a bag or clip to a backpack.
- PartyBoost compatibility offers a simple way to expand your sound system with other JBL speakers.
Cons
- As a renewed product, it may show minor cosmetic wear and does not come with the original manufacturer's full warranty.
- The 0 listed customer reviews for this specific renewed listing means there is no user feedback to gauge seller reliability or product condition.
The JBL Flip 6 (Renewed) is best for outdoor enthusiasts and casual listeners who want a proven, waterproof portable speaker at a reduced cost. Its IP67 rating and 12-hour battery are genuine advantages for poolside, hiking, or travel use. However, as a refurbished item, it is not ideal for buyers seeking a brand-new product with full manufacturer support, and the lack of reviews for this specific listing adds uncertainty about the seller's quality control.
Waterproof Rating: IP67 (dustproof and waterproof)
Battery Life: Up to 12 hours per charge
Dimensions: 2.8 x 7 x 2.6 inches
Weight: 1.21 pounds
Connectivity: Bluetooth wireless
Special Feature: PartyBoost for speaker pairing
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Frequently Asked Questions
How do I know if my trimmer has a left-hand reverse thread?
Nearly all modern string trimmers—gas and electric—use a left-hand reverse thread on the arbor bolt. The simplest way to confirm: if turning the bolt clockwise loosens it, it is a left-hand thread. If your trimmer’s owner’s manual specifies the thread direction, follow that. When in doubt, try turning clockwise first before applying excessive force in the wrong direction.
Can I replace a bump feed head with a fixed line head?
Yes, as long as the replacement head uses the same arbor thread size and type. Most fixed line heads and universal speed feed heads are designed to fit standard arbor sizes. However, verify the arbor diameter (commonly 10mm or 3/8″) before purchasing. The gearcase locking procedure and left-hand thread removal remain identical regardless of head type.
Why does my trimmer line keep melting inside the head?
Melted trimmer line is caused by friction heat when the line contacts hard surfaces (concrete, rock, metal) at high RPM, or when using line that is too thin for the trimmer’s power output. Upgrade to a thicker, higher-quality line (.080″ or .095″ instead of .065″), avoid running the trimmer at full throttle against hard surfaces, and ensure the head is not overwound, which increases internal friction.
Do I need a locking pin to replace the trimmer head, or can I improvise?
A dedicated arbor locking pin is ideal, but a small screwdriver, hex key, or drill bit of the correct diameter (typically 3/32″ to 1/8″) works effectively. The key requirement is that the tool fits through the gearcase alignment hole and engages the internal gear to prevent rotation. Never attempt to hold the spinning head by hand while loosening the arbor bolt—this is dangerous and ineffective.
How often should I replace my string trimmer head?
A quality trimmer head should last 2–5 years with regular residential use. Replace the head when the bump mechanism no longer advances line, the housing cracks, the eyelets become excessively worn (causing line to bind), or the drive tabs strip and the head no longer engages the gearcase. Regular cleaning of melted line residue extends head life significantly.
For more hands-on benchmarks and buying recommendations, consult our guides on residential zero-turn lawn mower guide, as well as durable ride-on lawn tractor guide, as well as automated robotic lawn mower guide.
