How to Put String Into a Weed Eater

Before you put string into a weed eater, switch it off and wait for the head to stop. Remove the battery, unplug a corded unit, or leave a gas engine off and pull the spark-plug boot if you will work at the head. On a typical bump-feed head, open the cap, wind line with the molded arrows, thread the eyelets, and close the head. Check the marks on your spool and the owner’s manual—head type and winding direction vary.

Make the trimmer safe before you touch the head

A string trimmer will not cut until trimmer line extends from the cutting head and can feed or stay locked in place. The same spinning head that cuts grass can also throw broken line, grit, and the cap itself if it is loose. Disable the tool before you open anything.

Put the power switch off and wait until the cutting head is fully stopped. Then isolate the energy source that matches your machine:

• On a battery model, remove the battery pack and keep it away from the housing so it cannot be clicked back in by accident.
• On a corded electric unit, unplug the cord from the outlet. Switching off alone is not enough if the plug is still live.
• On a gas weed eater, leave the engine off. If your hands will be on the head, disconnect the spark-plug boot as an extra precaution so a tug on the starter or residual ignition is less likely to fire the engine. How that boot comes off and goes back on is model-specific; follow the owner’s manual rather than forcing a connector.

Do not treat a “cool enough to touch” guess as a substitute for lockout, and do not open the fuel system or carburetor to reload line. Those jobs are unrelated to putting string in the head.

Wear eye protection. Line ends can spring out of a spool, and debris can still sit under the housing. Gloves are reasonable if the monofilament is stiff or the eyelets are packed with grass. Keep the cutting guard on unless the manual says you must remove it to reach the cap. Reloading a consumer head usually does not require taking the guard off, and the guard often carries the line cutoff blade that trims excess after the head is spinning again.

Identify the cutting head you actually have

Weed eater, string trimmer, and line trimmer all describe the same kind of consumer tool. The part that actually holds the string is the cutting head, and that head is not one design. Winding a bump-feed spool when you actually have a fixed-line or through-hole head wastes time and can break parts.

Look at the bottom and the sides of the head before you pry anything:

• A spring-loaded button on the bottom is usually a bump knob. That is the hallmark of a bump-feed head: you tap the knob on the ground while the head is spinning so a little line can pay out through the eyelets.
• Molded winding arrows and a removable inner spool usually mean the head is meant to be rewound with bulk trimmer line.
• A sealed or labeled cartridge that drops in as a unit is a pre-wound cartridge. You replace the cartridge instead of winding by hand.
• Short, pre-cut pieces locked into slots or clips, with no rewindable spool, point to a fixed-line head.
• A straight path through the housing that lets you push a single length of line from one eyelet to the other is a through-hole or quick-load design. You often wind that line with a knob or by rotating the head rather than lifting a spool out.
• An auto-feed head may look similar to a bump-feed unit but advances line without a ground tap, or with a different internal clutch. Some auto-feed heads still use a rewindable spool; others use a cartridge. Do not assume every auto-feed head rewinds like a bump-feed spool.

Turn the empty spool and the inside of the housing in good light. Winding arrows, line-size stamps, and the path from each channel to each eyelet are often molded into the plastic. Those marks, plus the owner’s manual, are the authority for your tool. This article describes common consumer patterns. It is not a substitute for a model diagram, and it does not name one head as universal.

Choose line diameter, shape, and how much to cut

Use the line diameter stamped on the spool, the cutting head, the cutting guard, or listed in the manual. That mark is the specification that matters. There is no single default size that fits every consumer trimmer.

Line that is too thick can refuse to pass the eyelets, bind inside a dual-line channel, or stress the spool and cap. Line that is too thin can break at the eyelet, whip apart in grass, or heat-weld into a solid mass on the spool because it packs tightly and rubs. If the head also specifies a shape, stay with a shape that will still pass the eyelet. Round monofilament is the most common. Twisted and multi-sided profiles trade stiffness, wear, and noise in different ways; none of those tradeoffs is a reason to ignore the printed diameter.

How much to cut depends on the head, not on a universal length in feet or meters. Some spools have fill marks or a “do not overfill” ridge. Stop there. An overfilled spool binds, especially on dual-line designs where each tail needs its own channel. If the head has no fill mark, wind only as much as sits evenly below the rim of the spool so the cap can close without crushing the wraps. Save leftover bulk line on the original spool rather than forcing extra wraps into the head.

Old line that has sat in sun or a hot shed can be brittle even when the diameter is correct. If a short test bend snaps instead of flexing, discard that piece and use fresher line of the same marked size.

What to have on hand

You do not need a full toolbox for most consumer bump caps. Have the following nearby so you are not hunting parts with the head half open:

• Trimmer line in the diameter marked on the head, guard, spool, or manual
• Eye protection
• Optional work gloves
• Optional needle-nose pliers to fish a short end through an eyelet
• A clean rag to wipe grass and grit out of the housing

Many bump-feed caps release by squeezing tabs or giving the cover a quarter-turn. Some retain the cover with a screw or small clips. Use the fastener you actually see; do not assume every cap is hand-only, and do not invent a driver size. Support the shaft so the spring and bump knob cannot drop into the grass when the cap comes off.

Replace parts instead of forcing them if the spool is cracked, the bump knob is rounded or seized, the spring is missing or collapsed, or an eyelet is melted into an oval. Rewinding good line onto a broken head will not restore feed.

Reload a typical bump-feed spool

The sequence below is typical for a consumer bump-feed head with a removable spool. Treat every step as a pattern to match against the arrows and notches on your head. If the physical parts do not match, stop and use the method for that design.

Open the cap without losing the spring

Support the trimmer so the cutting head faces up or rest the shaft so parts cannot roll away. Press the release tabs or unscrew the cap, then lift the cover straight off. Note where the spring sits before you move anything. On many heads the spring is under the spool or captured in the bump knob. Set the cap, spring, and knob in the same order they came off.

Lift out the old spool. Pull leftover line off and discard it if it is welded, flattened, or shorter than the eyelets need. Clean packed grass, sand, and melted nylon from the housing and from both eyelets. A blocked eyelet is one of the most common reasons a freshly wound head will not feed.

Seat the line and wind with the arrows

Read the winding arrows on the spool or the inner housing. Wind in that direction. Winding against the arrows is a frequent cause of a bump knob that feels dead after reassembly.

On a single-line spool, seat one end in the hub slot or through-hole the spool provides, then wind the rest in even, tight wraps. Keep the line under light tension so coils cannot slump into a loose pile.

On a dual-line spool, use the divider or the pair of hub holes the spool was molded with. Each tail should stay in its own channel. If the design uses one piece of line folded at the midpoint, seat the fold in the hub and wind both tails together, still keeping them from crossing. Do not chase a set number of turns; stop when the spool is filled to its marks or just below the rim.

If the spool has temporary holding notches on the rim, clip a short end into each notch after winding. Those notches exist so the line does not unwind while you aim the ends at the eyelets.

Thread the eyelets and close the head

Line each end up with the matching eyelet in the housing. Feed the ends through while you lower the spool onto the shaft so the spring and bump knob stay aligned. If an end slips back inside, use pliers to pull it through rather than spinning the spool and crossing the wraps.

Seat the spool fully. Reinstall the spring if you removed it. Put the cap on and turn or snap it until it is fully latched. A cap that only feels “mostly on” can fly off when the head reaches speed. Pull the two ends so they are roughly even, then confirm nothing is pinched between the cap and the housing.

Single-line versus dual-line channels

A dual-line spool is built so two cutting ends exit opposite eyelets. The divider, split hub, or pair of holes is there to keep those ends from occupying the same space. Crossed wraps act like a knot: the bump knob may click, but the line will not pay out.

Some dual-line heads take two separate lengths. Others take one length folded in half and wound as two tails. Both patterns are normal. What is not normal is mixing the two ideas on a spool that only has one style of hub. If you see a single slot and a single exit, treat it as a single-line spool and do not invent a second eyelet path.

Keep wraps tight and stacked, not piled in a cone. Loose coils migrate under neighboring wraps as soon as the head spins. That is another way line welds or locks. After the cap is on, a gentle pull on each exposed end should take out slack without unwinding the whole spool. If one side will not move at all, open the head and look for a crossed wrap before you start the engine or motor.

Through-hole and fixed-line heads are loaded differently

Abandon the bump-feed rewind as soon as the head has no removable rewindable spool.

On a through-hole or quick-load head, align the inner path so you can see daylight from one eyelet to the other. Push a single length of the correct diameter through until the two ends are about even. Then wind with the knob, or rotate the head, in the direction marked on the housing. You are still putting string into a weed eater, but you are not lifting a spool out first. Do not keep turning after the head feels full or after any fill indicator the housing provides.

On a fixed-line head, use pre-cut pieces of the length and diameter that head is designed to lock. Push each piece into its slot or clip until it seats. If a piece will not lock, it is the wrong size or the holder is worn. Forcing a random scrap of bulk line into a fixed slot is how holders crack.

If your trimmer uses a pre-wound cartridge, install the cartridge the housing was molded to accept. Winding bulk line onto a cartridge core that was never meant to be serviced is guesswork. When the manual says to replace the cartridge, replace it.

Auto-feed heads that use a rewindable spool may still follow the bump-feed winding pattern, including arrows and dual channels. Auto-feed heads that do not expose a spool should be loaded the way that housing is built—cartridge, through-hole, or fixed pieces—not by prying until something comes loose.

Reassemble, set the free length, and test feed

Before any restart, walk the assembly once:

• The spring is present and the bump knob can move if the head is bump-feed.
• The spool is fully down on the shaft and not sitting on a loop of line.
• The cap is fully latched or threaded.
• Each cutting end exits its eyelet and the ends are roughly even.
• The cutting guard is in place.
• The battery pack is still out, the cord is still unplugged, or the spark-plug boot is still off until you are ready to run.

There is no single leftover length that is correct for every head. If the guard has a molded line cutoff blade, that blade is what shortens excess after the head is up to speed. Leaving wildly long tails is a hazard because they can whip or break before the blade trims them. Leaving tails so short that they barely clear the eyelets means you have nothing to cut with until you feed more line.

Restore power only after the head is closed. Put on eye protection, keep bystanders and pets clear, and start the trimmer the way the manual describes. To bump-feed, tap the bump knob on soil or grass while the head is spinning. Avoid using pavement as the tap surface if you can; hard ground wears the knob and can shatter brittle line. Do not expect a fixed number of taps to equal a set feed length. If nothing comes out after a few firm taps, stop, disable the tool again, and open the head. Continuing to slam a jammed knob only damages the spring and the button.

If the string will not feed or keeps breaking

When a reload fails, the cause is usually mechanical, not mysterious. Work through the common faults before you replace the whole trimmer.

• Wound the wrong way. Open the head and compare the wraps with the winding arrows. Reverse the wind if they disagree.
• Overfill or a cone of loose wraps. Strip the spool and rewind below the fill mark with even tension.
• Crossed dual lines. Separate the tails into their channels or refold a single length so the midpoint sits in the hub.
• Blocked or melted eyelet. Clean the hole. If the plastic is oval or glazed, the head may need replacement.
• Wrong diameter or shape. Thick line jams; thin line breaks or welds. Go back to the stamped size.
• Missing, weak, or misaligned spring. A bump-feed head cannot release line without that spring and a bump knob that can travel.
• Old, brittle monofilament. Sun-baked line snaps at the eyelet even when the wind is correct.
• Heat-welded nylon. Friction inside a tight, dirty, or overfilled spool can fuse wraps into a puck. Cut the mass off and start clean. This is a known failure mode, not a reason to keep running a smoking head.
• Cracked spool or rounded bump knob. Replace the worn part. Forcing a cracked spool closed will not restore feed.
• Wrong head type. A fixed-line or through-hole head will never behave like a rewindable bump-feed spool. Use the insertion method that matches the hardware.

If line still will not pay out after a correct rewind, or if it snaps at the eyelet on every start, replace the spring, the spool, or the complete cutting head according to the manual. Persistent feed failure is a parts problem, not a reason to keep adding more line.

Limits: manuals, line size, and what this guide cannot settle

Head type, wind direction, line diameter, and fastener style vary across consumer trimmers. The molded marks on the spool and housing, and the manufacturer’s instructions for that model, override any generic how-to. This article cannot settle a model-by-model disassembly sequence, an official rewind diagram, a required line shape for a named product, or whether a particular aftermarket line is approved for a given engine or battery platform.

A correct reload does not remove the remaining hazards. The head can still throw line and debris. A cap that was not fully seated can come off in use. A gas engine can still start if the ignition is not disabled while you work. Keep the guard on, wear eye protection, and stay clear of the cutting path when you test feed.

Out of scope here are carburetor or fuel-system work, converting a string head to a blade, servicing commercial multi-string heads, and any claim that one line brand lasts longer or cuts cleaner. If the head is damaged, the shaft is bent, or the manual calls for a procedure you cannot identify from the parts in front of you, stop and use the model instructions or a qualified repair shop.

Frequently asked questions

Do I have to remove the cutting guard to put string in a weed eater?

Usually no. Leave the guard on unless the manual says it blocks the cap. The guard protects you and often includes the cutoff blade that trims long tails after the head spins.

How do I know which way to wind the spool?

Use the winding arrows molded into the spool or housing. If there are no arrows, check the manual. Winding against the intended direction is a common reason a bump-feed head will not release line.

Can I use any trimmer line I have in the garage?

Only if it matches the diameter marked on the head, spool, guard, or manual, and only if it can pass the eyelets. Random leftover line that is thicker, thinner, or a shape the eyelet cannot accept will jam or break.

Why does the bump knob feel dead after I reassemble the head?

Typical causes are the wrong wind direction, overfilled or crossed wraps, a blocked eyelet, or a spring that was left out or seated crooked. Disable the tool and open the head rather than tapping harder.

Is reloading different on battery, corded, and gas trimmers?

The string path is about the cutting head, not the power source. What changes is lockout: remove the battery pack, unplug the cord, or keep a gas engine off and disconnect the spark-plug boot before your hands are on the head.

When should I replace the whole head instead of just the line?

Replace the spool, spring, or complete head when the spool is cracked, the spring is missing or weak, an eyelet is melted, the bump knob will not move, or the head is a fixed-line or cartridge design that no longer locks pieces in place.