Quick Answer: How to Change String on a Weed Wacker
Turn off the trimmer and disconnect the power source — remove the battery, unplug the cord, or shut off the engine. Press the tabs on the cutting head, pull off the spool cap, remove the old line, wind fresh trimmer line in the direction marked on the spool, thread the ends through the eyelets, and snap the cap back on. Pull the line until it feeds freely before you resume cutting.
What You Need Before You Start
Gathering materials before touching the trimmer prevents stopping mid-task with a disassembled head.
- Replacement trimmer line — correct diameter for your model (see the gauge table below)
- Scissors or line cutters — to trim line to length after reassembly
- Work gloves — fresh trimmer line has sharp edges
- Owner’s manual or model number — confirms head type and line spec
Power Source Safety by Trimmer Type
- Battery / cordless trimmer: Remove the battery pack completely before touching the head. A bump or accidental trigger can spin the head even mid-restring.
- Corded electric trimmer: Unplug from the outlet — not just the power switch. Switches fail.
- Gas trimmer: Turn the engine off, wait for the head to stop completely, and let it cool if you ran it recently. Some technicians also disconnect the spark plug wire for full lockout.
What Size Trimmer Line Do You Need?
Line diameter is the most common purchasing mistake. Using line that is too thick jams the spool; line that is too thin snaps instantly on heavy vegetation. The correct diameter is printed on the spool cap or in the owner’s manual.
| Line Diameter | Trimmer Class | Best For |
|---|---|---|
| 0.065 in | Light-duty electric / battery (under 20V or 20cc) | Thin grass, lawn edging, light weeds |
| 0.080 in | Mid-range battery (20V–40V) or light gas | Mixed grass and moderate weeds |
| 0.095 in | Heavy-duty gas (25cc–30cc+) or high-voltage battery | Dense weeds, brush, thick overgrowth |
| 0.105 in and above | Commercial gas trimmers | Heavy brush, commercial clearing |
Source: Oregon Products line selection specifications and STIHL trimmer product documentation.
How to Identify Your Cutting Head Type
Following the wrong set of steps damages the spool or leaves you with a head you cannot reassemble. Identify your head type first.
Bump-Feed Head
The most common residential type. A spring-loaded spool sits inside a plastic housing. Tapping the head on the ground (bumping) advances line through one or two eyelets. The spool is removable for rewinding. Look for a rounded cap on the bottom of the cutting head with a bump knob at its center.
Single-Line vs. Dual-Line Bump Head
- Single-line: One eyelet on the head, one strand of line exits. Winding is simpler — one continuous length wound onto one side of the spool.
- Dual-line: Two eyelets, two strands exit opposite each other. The spool has two chambers or one chamber with a center anchor notch. Common on mid- to heavy-duty trimmers.
Fixed-Line / Pre-Wound Spool Head
No rewinding required. The entire spool is a sealed pre-wound unit — when the line is gone, the whole spool is discarded and replaced. Common on Greenworks models and select Ryobi battery trimmers. The head itself usually twists off or releases with a single press of a tab.
Brand Quick Reference
- Ryobi: Many models use a bump-feed dual-line head; newer EXPAND-IT and ONE+ models may accept pre-wound spools. Check the model page on ryobitools.com.
- STIHL: AutoCut heads are bump-feed dual-line; PolyCut heads use fixed plastic blades, not line.
- Husqvarna: T25 and T35 tap-advance heads are bump-feed dual-line.
- Echo: Speed-Feed 400 is a bump-feed dual-line head with a rapid-load design — line feeds from the outside without removing the spool.
- Greenworks: Many cordless models use drop-in pre-wound spools.
How to Replace Trimmer Line on a Bump-Feed Single-Line Head
- Disconnect power. Remove battery, unplug, or stop the engine. Confirm the head is fully stopped.
- Remove the spool cap. Press the two tabs on the sides of the cutting head simultaneously and pull the cap straight down. On some models the cap unscrews counterclockwise (reverse-threaded heads unscrew clockwise — check your manual).
- Remove the spool and old line. Lift the spool off the arbor (center post). Pull off all remaining old line. If line is fused or knotted, cut it free rather than forcing it — forcing it can crack the spool.
- Check the spool for damage. Inspect for cracks, worn eyelets, and a functioning spring beneath the spool. Replace the spool if cracked.
- Cut a length of new line. For a single-line spool, cut approximately 20–25 feet (6–7.5 m) of line at the correct diameter. Check the spool for a maximum-line indicator; overfilling causes the cap to not seat.
- Find the anchor notch. The spool has a small notch or hole near the center. Insert one end of the line into this anchor point to lock it in place.
- Wind the line. Wind in the direction indicated by the arrow molded onto the spool. Keep winds tight and even, layer by layer. Do not cross lines. Leave 6 inches (15 cm) of line free at the end.
- Thread the eyelet. Locate the eyelet on the trimmer head housing. Feed the free end of the line through it from inside the housing outward.
- Seat the spool and replace the cap. Hold the free line taut so it does not unwind. Press the spool onto the arbor, press the cap on until both tabs click, or screw it back on.
- Test feed. Pull the line to confirm it extends freely. Start the trimmer briefly and bump the head on a hard surface — the line should advance. Trim line to the cutting blade length marked inside the guard.
How to Replace Trimmer Line on a Bump-Feed Dual-Line Head
- Disconnect power. Same safety steps as above.
- Remove the spool cap and spool. Same tab-press or unscrew method. Note the position of the spring — it must return the same way.
- Remove all old line from both chambers. Dual-line spools have two separate winding chambers divided by a center rib, or one chamber with a divider notch.
- Cut two equal lengths of line — typically 9–12 feet (2.7–3.7 m) each, or use one 18–24 foot length and fold it in half. Some heads accept one long piece anchored at the midpoint notch.
- Anchor the line. If using two pieces, insert each end into its own anchor notch on its respective chamber. If using one long piece folded in half, seat the midpoint in the center anchor notch.
- Wind both strands in the same direction. Both strands wind the same direction as marked by the arrow on the spool — winding one strand opposite to the other is a common error that causes uneven feed and line breakage. OEM manuals for Ryobi and Echo dual-line heads explicitly note this.
- Keep both chambers even. Wind each side alternately in short segments so both finish with equal amounts of line. Uneven chambers cause one line to run out significantly faster.
- Leave 6 inches free on each strand.
- Thread both eyelets. Feed one free end through each of the two eyelets on opposite sides of the cutting head housing.
- Seat the spool, replace the cap, and test. Confirm both lines feed on bump.
How to Swap a Pre-Wound or Fixed-Line Spool
For users with pre-wound drop-in spools, rewinding is not part of the task. The process is a direct swap.
- Disconnect power.
- Remove the spool cap. Usually a single press of a center button or a quarter-turn counterclockwise.
- Lift out the empty spool. Discard the old spool — pre-wound spools are not refillable by design.
- Insert the new pre-wound spool. Orient it so the line exits through the eyelets. Most spools are keyed and only fit one way.
- Replace the cap until it clicks or locks.
- Pull the line ends through the eyelets if they did not self-feed, and test.
Important: Pre-wound spools are brand- and model-specific, not universally interchangeable. A Greenworks spool will not fit a Ryobi head and vice versa. Confirm compatibility using the model number on the trimmer body before purchasing. Greenworks and Ryobi both publish compatibility charts on their product pages and packaging.
Trimmer Line Type Selection Guide
Diameter is only one variable. Line profile (cross-section shape) affects cutting aggressiveness and noise.
| Line Profile | Cutting Performance | Best Use |
|---|---|---|
| Round | Moderate — smooth cut, longer wear life | General lawn maintenance, light weeds |
| Twisted / Spiral | Higher — aerodynamic shape reduces noise, cuts more cleanly | Grass and light-to-moderate weeds |
| Star-shaped / Multi-sided | Highest — sharp edges slice through thick stems | Dense weeds, overgrown brush |
Star-shaped and multi-sided line profiles cut more aggressively than round line because the sharp edges contact vegetation at higher force concentration per edge — a performance characteristic noted in Oregon Products’ trimmer line product specifications. However, star-shaped line wears faster and may break more frequently at the eyelet on light-duty heads not designed for it. Match profile aggressiveness to both vegetation type and trimmer power class.
How Long Does Trimmer Line Last?
Frequency of replacement depends on vegetation density, run time, and storage conditions. Trimmer line is made from nylon polymer, which degrades from UV exposure over time — stored line left in direct sunlight loses tensile strength and becomes brittle before it is ever used. Store bulk line in a sealed bag or container away from sunlight and heat. Some manufacturers recommend soaking new line in water for 24 hours before winding to increase flexibility and reduce breakage.
Common Mistakes and Troubleshooting
Line Won’t Feed When I Bump the Head
- Cause 1 — Line wound too tightly or overfilled: Excess line presses against the cap and cannot advance. Remove the spool, reduce line amount, and reassemble.
- Cause 2 — Line wound in wrong direction: The bump mechanism only advances line when wound in the correct direction. Unwind and rewind following the arrow on the spool.
- Cause 3 — Worn or broken spring: The spring beneath the spool pushes it down to advance line. A missing or collapsed spring prevents bump-feed from working. Replace the spring or full spool assembly.
Trimmer Line Welds or Fuses Inside the Spool
Fusing occurs when the line is wound too loosely, allowing strands to overlap and generate heat friction during high-speed rotation. It also occurs with line wound in the wrong direction — the strands bind against each other rather than feeding smoothly. Ryobi and Echo OEM manuals both cite incorrect winding direction as a primary cause of line fusing. Wind firmly and evenly, keep strands parallel, and always follow the directional arrow.
Spool Cap Keeps Popping Off During Use
- Cap tabs are worn or cracked — replace the cap.
- Spool is overfilled, creating internal pressure that forces the cap off — reduce line quantity.
- Cap was not fully seated — reassemble and confirm both tabs click before running the trimmer.
Line Breaks Immediately After Restringing
- Line diameter is too small for the trimmer’s power output — move up one gauge.
- Line exits the eyelet at a sharp angle — check that the eyelet grommet (the plastic or metal ring protecting the eyelet hole) is not cracked or missing. A bare metal edge cuts through line instantly.
- Line has been stored improperly and has become brittle from UV degradation — replace with fresh line from sealed packaging.
How Do I Know the Line Is Completely Used Up?
The trimmer loses cutting effectiveness noticeably — it takes multiple passes to cut what it previously handled in one. The bump mechanism produces a clicking sound but no line advances. Remove the cap and inspect the spool: if only a few inches of line remain anchored at the notch, the spool is empty and needs rewinding or replacement.
Frequently Asked Questions
Can I use any brand of trimmer line in my weed wacker?
For spools you rewind yourself, any brand of trimmer line at the correct diameter will work — trimmer line is not brand-locked. The critical variables are diameter and, secondarily, profile shape. Pre-wound drop-in spools are a different matter: those are brand- and model-specific and must match your trimmer’s cutting head dimensions.
Which direction do I wind trimmer line onto the spool?
Follow the arrow molded directly onto the spool face. Direction varies by manufacturer and model — there is no universal standard. Winding in the wrong direction causes line to fuse, prevents bump-feed from advancing the line, and can jam the spool inside the head. If the arrow is worn off, consult the owner’s manual or the manufacturer’s website using your model number.
How much line should I put on a trimmer spool?
Fill the spool to within 1/4 inch (6 mm) of the outer rim of the winding chamber — most spools have a molded MAX LINE indicator. Overfilling prevents the cap from seating and causes the line to bind. Under-filling means more frequent stops to reload. For most residential single-line heads, 20–25 feet (6–7.5 m) is typical; dual-line heads use 9–12 feet per chamber.
Do I need to soak trimmer line in water before using it?
It is optional but beneficial for round nylon line. Soaking for 24 hours before winding increases the line’s flexibility, which reduces snapping at the eyelet during use — particularly in dry or hot climates where nylon dries out quickly. Twisted and star-shaped co-polymer lines are less sensitive to this and do not require soaking according to most manufacturer guidance. Check the line packaging for the manufacturer’s recommendation.
