How to Refill Weed Eater String on a Typical Trimmer Head

To refill a typical bump-feed weed eater (string trimmer), isolate the power source, open the cutting head, remove leftover line, wind the correct diameter trimmer line in the direction marked on the spool, feed the free ends through the eyelets, reassemble the head, then test that the line advances. Head design, line size, length, and winding direction vary by model, so follow the arrows on the spool and the tool’s instructions whenever they differ.

A weed eater is the everyday name many people use for a consumer string trimmer: a handheld cutter that spins nylon cutting line instead of a metal blade. When that line is gone, welded into a lump, or too short to reach the grass, the tool will spin without cutting. Refilling the head is a routine service job, not a motor repair. The same basic idea applies to many bump-feed and similar spool heads: make the tool inert, match the line to the head, wind it so it can pay out, and put every small part back in order. The details that change from model to model—how the cap comes off, which way the spool turns, and how much line the drum will hold—are the details that cause most failed rewinds.

Make the trimmer safe before you open the head

Open a live cutting head and you are working next to a spring-loaded drum, sharp line ends, and metal or plastic eyelets, all attached to a machine that can start if the trigger is bumped. Treat the first minute of the job as energy isolation, not as a race to get new string on the spool.

What you should wear

Wear eye protection before you touch the head, and keep it on when you later test the feed. Cut line ends can spring outward, packed grit can fly from the eyelets, and a test start can throw leftover debris. A face shield is reasonable if you already use one for trimming. Close-fitting gloves help when you pull fused line or handle a metal eyelet, but they are not a substitute for keeping fingers off a head that is still spinning. Keep bystanders, children, and pets well away from the work area. Do not service the head while it is resting on your lap or pointed at anyone.

How to isolate a gas, electric, or battery trimmer

The goal is the same on every power type: the cutting head must not be able to start while your hands are inside it. How you get there depends on the machine.

• On a gasoline weed eater, stop the engine completely, set the tool down on a stable surface, and disconnect the spark-plug boot so a pull on the starter or a jostled switch cannot fire the engine. Do not rely on the trigger lock alone.
• On a corded electric string trimmer, release the trigger and unplug the power cord from the outlet or extension cord before you kneel down to the head.
• On a battery model, release the trigger and remove the battery pack from the tool. Do not leave a pack half-seated in the housing.

Follow any additional lockout or service steps printed in your owner’s manual. Those steps are model-specific and are not the same as a generic shop lockout procedure. If a control, plug, or battery will not isolate cleanly, stop and use the manual rather than improvising around a damaged switch.

Why the head must be fully stopped

A spinning trimmer head can keep moving after you release the trigger. Coast-down time is short, but it is long enough to cut skin or fling line. Wait until the spool, bump knob, and any remaining string are motionless. Then set the shaft so the head faces a clear, well-lit workspace. If the tool is hot from use, let the head and nearby plastic cool enough to handle. Heat-softened housings scratch and warp more easily when you pry at a stuck cap.

Identify the head type before you rewind

Not every cutting head is a rewindable bump-feed spool. Forcing one winding method onto the wrong design wastes line and can crack the housing. Look at the head itself before you cut a long piece of string.

How a bump-feed spool looks

Many consumer weed eaters use a bump-feed head. The usual clues are a spring-loaded bump knob on the bottom, a removable inner spool, molded winding-direction arrows, and one or two exit eyelets in the outer housing. When the line shortens, you tap the knob on firm ground while the head is spinning so a short length of line can slip out. Inside, the spool may be a single drum or a drum divided into two compartments for dual-line winding. Those compartments, notches, and arrows matter more than the color of the plastic.

Fixed-line, auto-feed, and quick-load heads

Other heads do not rewind the same way:

• A fixed-line head uses short, pre-cut pieces of cutting line that lock into slots or holes. You replace those pieces; you do not wind a long coil onto an inner spool.
• An auto-feed head still uses a spool in many designs, but line advances with a clutch or centrifugal mechanism instead of a bump on the ground. The rewind may look similar, yet the spring stack and spool orientation are easy to assemble backward if you ignore the marks.
• A quick-load or speed-feed head often lets you push a single length of line through the eyelets and wind it from the outside, sometimes without lifting the inner spool out of the housing. If the head has a through-hole path and a winding knob, read those features before you pry the drum apart.

None of these designs is universally “better.” They simply load differently. If you cannot tell which one you have, photograph the assembled head from the bottom and the side, then compare the picture with the parts diagram or the head chapter in the manual. Do not assume a brand name on the shaft tells you the winding method. Aftermarket heads are common, and the same tool family can ship with more than one cutting head over its life.

When to replace the head instead of rewinding

Rewinding only works if the housing, spool, eyelets, and retainer spring can still do their jobs. Replace the head, or at least the inner spool, when you see a cracked drum, a melted race where the spool should turn, bent or missing eyelets, a broken bump knob, or a spring that is bent, rusted flat, or missing. A head that will not stay closed after a careful assembly is also a parts problem, not a winding problem. Keep every clip, washer, and spring in a small tray in the order you removed them. Photographing the stack before you lift the spool is the cheapest way to avoid a rattle later.

Choose line that fits the head, not just the thickest roll on the shelf

Trimmer line is the consumable. The head is the mechanism that has to store it, grip it, and release it a little at a time. The allowed line diameter is printed on the head, the spool, a label on the shaft, or the owner’s manual. That marking is the specification that matters. A thicker coil on the store shelf is not automatically a better refill.

Where to find the allowed diameter

Check the molded text on the spool flanges and the inside of the cap first. Many heads repeat the size range on a sticker near the rear handle or along the boom. If those marks are worn off, use the manual or a parts list for that exact head, not a guess based on another trimmer in the garage. If two sources disagree, treat the marking on the head you are actually opening as the limit for that housing.

What happens if the line is too thick or too thin

Line that is too thick may not seat in the spool grooves, may refuse to pass the eyelets, or may jam the bump mechanism so nothing feeds. It can also stress a plastic drum that was never sized for that stiffness. Line that is too thin may rattle in the eyelets, weld more easily from friction heat, or break before it can cut. Either mismatch can look like a “bad rewind” when the real issue is diameter.

Round line is the common, widely available shape and is what most generic refill instructions assume. Shaped line—edged, twisted, or otherwise profiled—exists and will fit some heads if the diameter is still in range. Shape is not a guarantee of longer life or faster cutting, and a stiff profile can be harder to wind evenly. Stay inside the stated diameter and choose a shape you can wind without crossing layers.

Whether leftover line is worth saving

Do not rewind line that is cracked, sun-brittled, flattened into a permanent oval, or fused into a shiny lump from heat. Those pieces will snap at the eyelet or lock the coil so the bump knob does nothing. Short leftovers are useful only if they are still flexible and long enough to reach from the spool, through the eyelet, and a short working distance outside the head. When in doubt, start with fresh line of the correct diameter. Store unused coils out of direct sun and away from heat so the next refill is not already brittle.

Open the head and clear the old line

Once the tool is isolated and you know you are dealing with a rewindable spool, open the head in a way that preserves the small parts. There is no single twist direction that is safe to assume for every weed eater. Some caps use tabs, some unscrew, and some lift after you align marks on the bump knob and housing. If the plastic is printed with arrows or “open” icons, those marks override any generic advice.

How typical bump-head caps come off

Common patterns include:

• Squeezing or pressing two tabs on the cap and lifting the cover straight off.
• Holding the outer housing and unscrewing a cover or bump knob. The thread direction is not universal, so stop if the part tightens or the plastic begins to creak.
• Aligning a mark on the knob with a mark on the housing, then lifting the knob to release the spool.

Work with your hands or a tool that will not gouge the housing. If grass and mud have glued the cap in place, soak the packed debris with a little water or brush it out and try again. Prying hard on a thin rim is how bump heads crack. A seized head is a debris problem first, not a reason to twist with a large wrench.

Parts you should not lose

Under the cap you will often find an inner spool, a retainer spring, and sometimes a washer, plate, or clip. The spring is what lets a bump-feed head release line. If it walks off the bench and you close the head without it, the knob will feel dead and the line will not advance. Lay the parts out in removal order. Note which face of the spool was up; many spools have a drive feature, a “this side out” mark, or different flanges on each side. The outer housing usually stays on the shaft. You do not need to remove the entire head from the boom unless the manual says so or the housing itself is damaged.

What to inspect inside the housing

Pull out leftover line, including scraps hidden under the last coil. Clear grass, soil, and melted nylon from the eyelets with a wooden stick or a soft brush so you do not enlarge the holes. Look for:

• Cracks in the spool walls or the outer housing
• Bent, grooved, or missing eyelets
• A spring that is kinked, corroded, or no longer stands at its original height
• Sand packed in the bump-knob bore, which can keep the knob from moving

A dirty but intact head can go back into service after a careful rewind. A cracked or heat-damaged head should be replaced. Continuing to wind line into a broken drum only postpones the same jam.

Measure, cut, and wind single- or dual-line spools

Winding is the step that decides whether the head will feed or become a solid brick of nylon. The correct length is the length shown in the manual or molded on the spool. If that figure is missing, use a practical limit instead of inventing a universal footage: cut only as much line as the spool can hold in even layers without the coil rising above the rim, and leave enough free end to reach through each eyelet.

How much line to cut

Overfilling is one of the most common reasons a freshly refilled weed eater will not feed. A coil that stands above the spool flanges rubs the cap, binds on the spring, or locks against the housing. Underfilling is less harmful; you will simply reload sooner. If you are using a dual-line head, you may need two equal lengths or one long piece folded at the center, depending on whether the spool has a center slot. Follow the spool’s slots and dividers rather than a one-size-fits-all cut.

Which way to wind

Wind in the direction of the molded arrows on the spool or cap. Those arrows exist because the bump or auto-feed mechanism releases line in one direction only. Winding the opposite way is a frequent cause of a head that spins happily and never pays out string. There is no reliable “always clockwise” rule for every string trimmer, including tools sold under the everyday name weed eater. If one flange says one direction and the housing says another, stop and check the manual; do not split the difference.

How single-line and dual-line spools differ

A single-line spool is a single drum. Anchor the line in the start hole or slot, then wind a tight, even coil toward the rim. Keep the free end available at the end of the wind so you can send it through the single eyelet.

A dual-line spool is usually divided by a wall or uses two stacked paths. Each side is wound separately, or one piece is hooked at the center and both halves are wound in the marked direction. Both free ends must remain available. If one end disappears under the coil, that side will never reach its eyelet. Do not jump the divider and wind both lines as one messy pile. The divider is what keeps the two ends from tying themselves together when the head bumps.

How tight the wind should be

Keep the line snug so the coil cannot slump, but do not stretch it like a spring. Stretching thin line can make it oval and eager to weld. Lay each turn next to the last instead of crossing over earlier layers. A bird’s nest looks full and will not pay out. Pause every so often and press the coil down with your thumb so it stays below the rim. If the spool has parking notches on the flanges, tuck a short free end into each notch when the wind is finished. Those notches are there so the coil does not unwind in your hands while you walk the spool back into the housing.

Reverse winding, crossed layers, and an overstuffed drum are the three rewind mistakes most likely to produce a no-feed head. If any of those happened, unwind and start again. It is faster than assembling the tool and discovering the problem in the yard.

Thread the eyelets, seat the spool, and close the head

Reassembly is not just putting the cap back on. The spool has to sit on its arbor, the spring has to stand in line, and each free end has to leave through the matching eyelet before the cover locks.

Getting the ends through the eyelets

If the spool has parking notches, leave the short ends clipped there while you lower the spool into the housing. Align any drive lugs, flats, or tabs so they engage the arbor. A spool that sits crooked may spin without turning the line, or it may climb the spring and rattle the cap loose.

Route each free end out through the eyelet that matches its side of the drum. On a dual-line head the two paths should not cross inside the housing. Once the ends are through, release them from the notches. Pull just enough line so a short working length sits outside each eyelet. That tail only needs to be long enough to cut grass and to give the feed mechanism something to pay out. An extra-long pair of tails is not a specification, and whipping oversize loops on the first start can slap the shaft or weld against the housing.

How the spool should sit

The spool should drop onto the arbor without being forced. The spring belongs in its original order—usually under the spool or between the spool and the bump knob, depending on the head. It must stand upright. A spring pinched sideways will make the knob feel stiff or dead. If a washer or retainer was present, it goes back in the same place and facing the same way. Do not add extra washers to “take up slack.”

Knowing the cap is fully locked

Refit the cap or bump knob the way it came off, using the same tabs, threads, or alignment marks. The cover should seat fully around the rim. Tabs should click or rest in their pockets; a threaded cover should stop in a normal, even way without chewing plastic. Pull gently on the housing to confirm it is not hanging on one tab. Rotate the bump knob by hand if the design allows it. The knob should move a little against spring pressure and return. If the cap walks off when you tug the line, it is not locked. Open it and check for a trapped coil, a misaligned spool, or a spring sitting on the rim instead of in its bore.

Restore power and test the feed

A closed head is not a proven head. Test the feed in a clear area before you walk back into tall grass or fence line.

How to check feed without starting a full job

Reinstall the battery, plug in the cord, or push the spark-plug boot firmly onto the plug. Stand in an open spot, keep the cutting path away from people, glass, and loose gravel, and start the tool using its normal controls. Let the head reach its usual running condition. For a bump-feed head, use a light tap of the bump knob on firm, bare ground—not on rock, and not a series of hard slams. For an auto-feed head, use the feed cycle the tool already has; do not invent a bump if the head was not designed for one.

What a correct feed feels like

Line should advance a short amount and then hold. You should not empty the spool in one burst, and you should not have to hammer the head to get any movement. After the test, shut the tool down, isolate power again if you need to trim the tails, and cut the two sides to a matching working length if your head uses dual line. Equal tails keep the head from shaking.

When to stop and reopen the head

Shut the tool down and isolate power if nothing moves, if the head chatters or vibrates hard, if the cap starts to loosen, or if you smell or see line welding from heat. More force will not fix a coil that was wound backward or stuffed past the rim. Reopen the head and look for the mechanical causes in the next section. Repeated hard bumping on pavement is a good way to crack a knob that was only guilty of a rewind error.

If the line will not feed or keeps breaking

When a careful rewind still fails, stay with the cutting head. A no-feed or constant-break problem after a refill is usually mechanical, not a reason to diagnose the engine or motor.

Why the line stays stuck

Work through the common causes in this order:

• The coil was wound against the arrows, so the feed mechanism tries to tighten the drum instead of releasing it.
• Layers were crossed, or one end on a dual-line spool was buried.
• The spool was overfilled and the coil is rubbing the cap or spring.
• Old line fused into a lump from earlier heat and is now one solid ring.
• Grass or melted nylon is still packed in the eyelets.
• The retainer spring is missing, weak, or pinched, so the bump knob cannot move.
• The spool is cracked or the drive features are stripped, so the drum does not turn with the head.
• The line diameter does not match the head, so the coil cannot slip through the eyelets.

The fix is almost always a clean rewind, a cleared housing, or a new spool or head. Forcing a thicker line through a jammed eyelet makes the next failure more likely.

Why line snaps at the eyelet

Line that breaks at the exit hole is often old, wet from poor storage, or sun-brittled. It can also be sawing itself on a nicked metal eyelet or folding sharply because the coil is feeding at a bad angle. Inspect the eyelet edge. Replace a damaged head rather than dressing the hole aggressively and making it larger than the line can control. Fresh line of the correct diameter, wound in even layers, solves many “it keeps breaking” complaints that were really leftover scrap and a rough exit.

When the head itself is the problem

If you have rewound cleanly twice, the spring is present, the diameter matches, and the line still will not advance, treat the head as worn. Cracked spools, rounded drive lugs, and tired springs are ordinary wear parts. Replacing those parts, or the complete cutting head when the housing is damaged, is the appropriate next step. It is not a verdict on the rest of the trimmer, and it is not a reason to keep escalating bump force.

What this guide cannot replace on your exact model

This sequence is a model-agnostic path for common consumer bump-feed and similar spool heads. It is not a substitute for the markings on your spool or the service chapter in the owner’s manual. Winding direction, allowed line diameter, whether a cover unscrews left or right, the order of the retainer spring, and any quick-load path through the eyelets are manufacturer-specific. When a molded arrow, a label, or the model instructions conflict with a generic step, follow the part in your hand.

Use the manual or a parts diagram whenever the head uses an unfamiliar lock, whenever a fastener will not move without force, or whenever you are installing a different style of head than the tool originally wore. Compatibility, warranty, and replacement-part questions belong to the tool maker or a qualified service shop. This article also does not cover engine, motor, clutch, or shaft repair. If the trimmer will not run, overheats, or has a damaged boom, stop and have the machine inspected. A correctly refilled string trimmer should feed a short length of line and cut again. It will not become a new tool, and no rewind can promise that the next coil will never break.

Handled in that order—safe isolation, head identification, the right diameter of cutting line, a clean wind in the marked direction, eyelets threaded, and a gentle feed test—most everyday weed eater refills are a bench job you can finish before the grass gets ahead of you again.