To put trimmer line in a typical weed wacker, isolate power, identify the cutting head type, open the head, and remove leftover line. Load the diameter and length specified for your model, wind in the marked direction without crossing coils, and leave equal tails through the eyelets. Reassemble the head and confirm the line feeds. Exact size, length, and wind direction vary, so check the tool or manual before you cut line.
A consumer string trimmer, often called a weed wacker, cuts with replaceable polymer trimmer line held in a rotating cutting head. Most homeowner heads use a wound spool of monofilament line, not a permanently attached blade. The reload is straightforward once you match the procedure to the head in your hand. Head type, line diameter, cut length, and winding direction are model-specific, so treat the steps below as a general sequence and confirm the details printed on the tool or in the manufacturer’s manual before you cut line.
Safety first: isolate power and protect yourself
Do not open the cutting head while the engine or motor can still start. A weed wacker can throw leftover line, dirt, and chips of nylon the moment the head turns. Isolate power first, then wait until every moving part has stopped.
On a gas string trimmer, switch the engine off and let it cool enough to handle. Disconnect the spark-plug boot so an accidental pull of the starter cannot fire the engine while your hands are on the head. On a battery model, remove the battery pack for battery isolation. On a corded electric model, unplug the tool from the outlet. Do not rely on a trigger lock or a momentary switch alone.
Wear eye protection. Line fragments and yard debris can leave the head at high speed when you test the feed later. Sturdy gloves help when you pull fused nylon, handle metal eyelets, or work around the debris shield. The cutting head is still a cut hazard when the tool is off. Leftover line, sharp eyelet edges, and the rim of the debris shield can slice skin.
Work on a stable surface with the shaft supported so the head cannot roll or swing. If you remove the debris shield to see the head more clearly, set it aside in order and put it back before any test run. Keep children, pets, and bystanders away from the work area for both the reload and the first brief check.
Identify the cutting head before you buy or cut line
Not every weed wacker uses the same reload. Winding line into a bump-feed head is different from snapping short pieces into a fixed-line head or exchanging a sealed cartridge. Identify the design before you buy a bulk spool of monofilament line.
A bump-feed head is the most common homeowner pattern. The bottom of the cutting head has a spring-loaded bump knob. Tapping that knob on the ground while the head spins is meant to release a short length of line. The cover usually comes off to reveal a spool, and the spool often has molded winding arrows or the word “wind.” Many of these heads are dual-line, with two exit eyelets on opposite sides. Some are single-line, with one eyelet.
An auto-feed head also holds a wound spool, but it advances line by centrifugal force or an internal mechanism instead of a deliberate bump. The housing may look similar to a bump-feed head, so look for the absence of a working bump knob and for any markings that describe automatic feed. The winding rules are still usually printed on the spool, not on the marketing label of the tool.
A fixed-line head does not use a long wound coil. It accepts short, pre-cut pieces of trimmer line that lock into slots or channels. If you see several short ports around the rim and no large internal spool, do not try to wind a long length inside the housing.
A cartridge head or a system that only accepts a prewound spool is meant to be swapped as a unit. The cartridge may be sealed, or the replacement spool may drop in already wound. Forcing those housings open can break tabs and does not create a better feed.
Useful markings include the approved line diameter on the head, spool, or shaft decal; arrows or “this way” text on the spool; the number of eyelets; and any note that the head takes a factory cartridge only. If the housing is unlabeled in everyday language, use the model number on the shaft or motor housing and the current manufacturer manual or parts list rather than guessing from a similar-looking tool. When the head is clearly a sealed cartridge, or when the spool is sold only as a prewound replacement, stop and use that service method instead of hand-winding.
Choose line diameter, type, and a safe cutting length
Approved line diameter is commonly printed on the cutting head, the spool, or a decal on the shaft. That marking is the default choice. Using the size the manufacturer specifies for that head is more important than matching a size you used on a different weed wacker.
Line that is much thicker than the head allows may not pass the eyelets, may refuse to advance, or may overload the spool and motor. Line that is much thinner may break at the eyelet, slip in the anchors, or melt and weld in place from friction heat. Do not treat a size that “usually works” on another brand as interchangeable.
If the paper manual is missing, look first at the head and spool, then at the model number on the tool and the manufacturer’s current documentation. Consumer string trimmers are sold with a range of line diameters, so any size you hear described as typical is only an example to check against your markings, not a recommendation.
Length is also model-specific. Some manuals state a cut length for a full reload; some spools have fill lines or channel walls that show when the coil is full. If you have no length figure, cut a conservative piece, wind until the channel is evenly filled without climbing over the rim or burying the eyelets, and stop before the cover will no longer seat. It is safer to load a bit less and add line later than to overfill and bind the spool. Do not use a single universal foot or meter length for every head.
Most replacement line is monofilament line, a single-strand polymer. Round line is the common general-purpose shape. Shaped line (for example, square, star, or twisted profiles) is sold as an alternative cutting edge, but shape is not a guaranteed upgrade. Feed behavior, noise, and wear depend on the head, the vegetation, and whether the line actually fits the eyelets. Choose a shape only if it is compatible with your head and you accept that it may feed differently. Skip brand comparisons and pack-size shopping lists; fit and winding quality matter more than marketing claims about speed or toughness.
Open the head and clear old line
With power isolated, turn the tool so you can see the cutting head. Photograph or note the order of the cover, spool, spring, and any washer before you separate the parts. Bump-feed and many auto-feed covers come off in a few common ways: squeeze tabs on the sides, twist a locking ring, or remove a center screw or nut. There is no single correct fastener for every brand. Follow the markings on the housing. If a nut uses a standard right-hand thread, loosening is counterclockwise, but only treat that as a default when the tool does not show a different direction.
Not every head is meant to be opened by the user. If the cover has no obvious tabs, no twist lock, and no service fastener, stop and check whether the design is a sealed cartridge or a replace-only prewound spool.
Lift the cover straight off so you do not bend locking tabs. Remove the spool. If a spring sits under the bump knob or under the spool, keep it oriented the way you found it. A missing, inverted, or damaged spring is a frequent reason a bump-feed head will not advance line later.
Pick out leftover monofilament, welded nylon, packed grass, and grit. Fused line in the channel or in an eyelet will keep new coils from sitting flat. Inspect the eyelets. If they are collapsed, cracked, or worn to a sharp burr, new line will fray or snap at the exit even when the wind looks neat. Check the spool for cracked flanges, a broken divider on a dual-line spool, and worn anchor slots. If the spool, spring, bump knob, or housing is cracked, or if the bump mechanism is stuck solid, replacing the cutting head is safer than improvising a repair.
Wipe the inside of the housing so dirt does not pack under the new coils. Do not grind, drill, or enlarge eyelets to force a thicker line through. Refit the debris shield later if you removed it; do not run the tool with the shield off.
Insert and wind the line so it will feed
The goal is a tight, even coil that can turn inside the housing and pay out through the eyelets without crossing itself. Follow the winding arrow or molded “this way” text on the spool. Winding against that direction is one of the most common causes of a head that will not feed.
Dual-line heads typically keep the two sides of the line in separate channels or on opposite halves of a divided spool, and they need two tails of similar length exiting opposite eyelets. Single-line heads use one continuous coil and one working tail. The head in front of you determines which method applies; the two approaches below are alternatives a spool may require, not interchangeable tricks.
One-piece dual-line winding
Many dual-line spools have a through-slot or notch across the hub. Fold a single length of trimmer line so the midpoint sits in that slot, then wind both halves at the same time in the direction of the arrows. Keep each half in its own channel. The coils should lie flat, stacked, and snug. Do not cross one side over the other. Do not wind so loosely that the line springs off the spool when you set it down, and do not wind so tightly that you crush or flatten the monofilament.
Stop when the channels are evenly filled and the remaining ends are long enough to reach through both eyelets with a short working tail outside the housing. Hook or clip those ends into the temporary holding notches on the spool rim if the spool has them. Those notches exist so the tails stay put while you drop the spool back into the head.
Two-piece winding
Some spools have two separate anchor holes instead of a through-slot. Cut two pieces of similar length, or cut one piece and divide it. Push one end of each piece into its anchor hole until it catches, then wind each half in the marked direction, again keeping the coils in their own channel. The finished tails should still be long enough to pass through the opposite eyelets. If one side is much longer than the other, the head will run out of balance and one eyelet will go empty first.
Single-line and fixed-line heads
On a single-line spool, anchor one end in the single hole or slot and wind the rest as one coil in the direction of the arrow. Leave one tail long enough to pass through the single eyelet.
On a fixed-line head, do not wind a long coil at all. Use pieces cut to the length the head is designed to hold, or use the pre-cut pieces sold for that design. Push each piece into its locking slot until it seats. Equal projection on both sides of a through-slot design keeps the head balanced. If a piece will not lock, it is the wrong length or diameter, or the slot is worn.
For any wound spool, overfilling is as harmful as winding the wrong way. If the last coils climb over the flange, bury the holding notches, or make the cover rock, unwind a few turns. Crossed winds, a mound in the middle of the spool, and line trapped under an earlier coil will bind as soon as the head tries to pay out.
Reassemble the head and confirm the line advances
Keep power isolated until the cutting head is fully closed. Seat the spring first if the design uses one, in the same orientation you noted during disassembly. Set the spool into the housing so the temporary holding notches, if present, line up with the eyelets. Thread each tail through its eyelet, then release the tails from the holding notches so they can feed. The tails should be long enough to extend outside the housing; tails that end inside the eyelet will not catch when you bump or auto-advance.
Align the cover with the eyelets and lock the tabs, twist lock, or center fastener completely. A cover that will not seat usually means the spool is overfilled, cocked, assembled in the wrong order, or sitting on a spring that is not in its pocket. Confirm that a bump knob, if the head has one, can move. It should depress and return instead of sitting rigid or falling out.
Refit the debris shield if you removed it. Restore power only after the head is complete: reconnect the spark-plug boot on a gas unit, or reinstall the battery or plug in a corded unit.
Test feed in a clear area with bystanders well back and eye protection on. For a bump-feed head, a gentle tap of the bump knob on bare soil while the head is spinning is the usual check; do not slam the head on concrete or roots. For an auto-feed head, a brief run in open space is enough to see whether line moves out of the eyelets. A successful reload looks balanced, with similar tails on a dual-line head, and the line should lengthen a little when you advance it rather than staying locked or exploding out in a tangle. Do not spin the head toward people, windows, or hard objects. There is no guaranteed bump technique, run time, or speed that proves the rewind on every model. A correct wind also does not guarantee the line will never weld or jam later under heat and heavy grass.
When your model does not match the generic steps
Some cutting heads are not designed for hand winding. If the head is a sealed cartridge, or if the manufacturer only lists a prewound spool as the replacement, install that part instead of prying the housing apart. Forcing tabs on a cartridge head can break the feed mechanism and leave you with a tool that will not accept the next genuine replacement either.
If the paper manual is gone, read the model number on the shaft or motor housing and use the manufacturer’s current manual or parts list for line size, wind direction, and whether the head is user-serviceable. Third-party photos can be useful for recognizing a bump knob versus a slot-style fixed-line head, but they are not authority for a named model’s official diameter or disassembly order.
Stop and replace the head, or have the tool serviced, when the housing is cracked, the bump mechanism is seized, fasteners are rounded, eyelets are destroyed, or the cover will not lock even with a correctly filled spool. Improvised repairs, missing springs replaced with random hardware, and drilled-out eyelets create new failure points. Proprietary commercial heads and some quick-load systems also fall outside this generic sequence; if the parts do not match the description of a serviceable spool, do not force the procedure.
Troubleshooting a head that will not feed or keeps breaking line
If newly installed line will not advance, unwind and inspect before you assume the trimmer itself has failed. Check these mechanical causes first:
- The spool was wound against the winding arrow.
- Coils are crossed, loose, or piled above the flange.
- The spool is overfilled, so it cannot turn in the housing.
- The line diameter is too large for the eyelets or too small to stay anchored.
- The spring is missing, inverted, or broken on a bump-feed head.
- An eyelet is blocked by welded nylon, grass, or a collapsed metal ring.
- The tails were too short to pass through the eyelets and catch.
- The cover, spool, and spring went back in the wrong order, so the bump knob cannot move.
Line that snaps at the eyelet often met a sharp or damaged exit, was the wrong diameter, or was already nicked from a previous break. Line that “welds” inside the spool is a common description of melted nylon from heat and friction, not a laboratory diagnosis. Heavy grass, a stalled head, and undersized line packed tightly in a hot housing can fuse coils together so they cannot pay out. Unwind the fused mass, clean the channel, and reload with the specified diameter. Do not use solvents or a heat gun as a standard way to free welded line; those methods can damage the spool and housing.
If the cover pops off in use, the tabs were not fully seated or the spool was too full. If one side of a dual-line head empties while the other stays full, the halves were not wound evenly or one tail never entered its eyelet. If the bump knob feels dead, open the head and confirm the spring is present and oriented correctly.
Do not expand the job into engine, carburetor, or motor diagnosis from a feed problem alone. A head that is correctly wound, correctly sized, and mechanically complete should at least release line when you advance it. Persistent breakage after a clean rewind, a cracked housing, or a head that still will not open or close as designed is a reason to replace the cutting head or take the tool to qualified service rather than keep forcing line through a damaged path.
Quick reload checklist
Use this sequence as a memory aid, then confirm model-specific size, length, and direction on the tool or in the manual:
- Stop the weed wacker completely. Disconnect the spark-plug boot, or remove the battery or unplug the cord.
- Put on eye protection and gloves. Treat the head, eyelets, and debris shield as sharp.
- Identify bump-feed, auto-feed, fixed-line, or cartridge construction before you cut line.
- Open the cover using the tabs, twist lock, or fastener on that housing. Note the order of cover, spool, and spring.
- Clear old line, dirt, and fused nylon. Replace a cracked spool, failed spring, or ruined eyelet instead of reloading into damaged parts.
- Cut monofilament line to a conservative length that matches the specified diameter. Do not overfill.
- Anchor the line in the through-slot or holes. Wind with the arrows, keeping dual-line halves separate and coils flat.
- Leave tails long enough to pass through the eyelets. Seat the spring and spool, route the tails, and lock the cover.
- Refit the debris shield. Restore power only when the head is closed.
- Advance the line in a clear area and confirm it feeds before you return to trimming.
Putting trimmer line in a weed wacker is a parts-matching job more than a strength job. Isolate power, identify the cutting head, use the marked line size, wind in the marked direction, and keep the coils flat. When the head in your hand is a sealed cartridge or a damaged assembly, install the intended replacement instead of forcing a generic rewind.
