To restring a line trimmer, fully isolate the tool from power, open the cutting head, and either rewind fresh line onto the existing spool in the marked direction or install a compatible pre-wound spool. Thread the ends through the eyelets, put any spring, washer, and cap back in the same order, then leave only a short working length of line so a bump-feed or auto-feed head can advance it after you reassemble and restart the tool safely.
What restringing involves
Restringing a line trimmer—also called a string trimmer—means putting new cutting line into the existing trimmer head so the tool can cut again. It is routine maintenance of the cutting end, not a repair of the motor, engine, shaft, or drive. When the line is gone, fused, or too short to feed, the head still does its job if you can load fresh line and close it correctly.
Two paths are valid. You can rewind bulk trimmer line onto the spool that is already in the head, or you can drop in a matching pre-wound spool or cassette. Rewinding is the usual job when the plastic spool is intact, the head is a common bump-feed design, and you have line of the diameter the head is built to accept. A pre-wound unit is often simpler when the old spool is cracked, the head is sold only as a sealed cassette, or you prefer not to hand-wind.
This guide covers general consumer restringing on common bump-feed and similar dual-line heads, including rewind-in-place and replacement-spool paths. It is not a brand manual. Head design varies: bump-feed, auto-feed, fixed-line, and proprietary cassettes do not all open or load the same way. Markings on the spool or hub, and the owner’s manual for that model, always override a generic sequence.
Restringing is also different from replacing a cracked head, worn eyelets, a seized bump knob, or the whole cutting assembly. If the housing is split, the spring is missing, or the head no longer matches a simple cap-and-spool pattern, loading new line will not restore a safe cutting tool. In those cases you need the correct replacement part or a qualified shop, not another rewind.
Make the trimmer safe before you touch the head
Do not open the head while the tool can still spin or start. Isolate it from power first, then wait until every moving part has stopped. A spinning line, a live switch, or a hot muffler can injure you before you ever touch the spool.
Power-type shutdown
- Battery trimmer: Switch the tool off, remove the battery pack, and keep the pack away from the work area so it cannot be reinserted by accident.
- Corded electric trimmer: Switch off and unplug the cord from the outlet. Do not rely on the trigger lock alone.
- Gas trimmer: Switch the engine off with the normal stop control and wait until the cutting head is motionless. Let a hot engine and muffler cool before you handle the head or rest the tool on your lap. On many small engines, disconnecting the spark-plug boot is a typical extra isolation step so the engine cannot start if the shaft is turned; confirm that practice in the owner’s manual for your chassis rather than treating it as a universal rule.
Do not invent a timed cooldown, drain fuel, or bypass guards and interlocks. If the manual describes a different isolation sequence, follow that sequence.
Hands, eyes, and the work surface
Cut line, coil springs, and metal eyelets can snap or cut. Wear eye protection and gloves. Keep loose clothing and jewelry away from the head. Work on a stable, well-lit surface with a tray or towel so the spring, washer, cap, and line tails cannot roll away. Support the head when the cap comes off; many consumer heads store a compressed spring under the spool, and that spring can jump if you pull the cover straight toward your face.
Identify the head type and the line it accepts
Head design is the main reason a generic rewind either works or fails. Look at the bottom and inside of the head before you cut any line.
Visual clues, not brand names
- Bump-feed head: A knob or button on the bottom of the head. With the head spinning, tapping that bump knob on the ground is how many consumer trimmers pay out more line. Inside, you usually find a spool, a spring, and two exit eyelets.
- Auto-feed head: Line advances by an internal mechanism rather than a deliberate bump. The outside may lack a prominent bump knob, or the manual will describe automatic feed. Do not assume bump technique applies.
- Fixed-line or single-piece head: Short, preformed pieces of line lock into slots or holes. There is no rewindable spool. You replace the pieces, not wind a coil.
- Cassette or proprietary cartridge: A sealed or semi-sealed unit that drops in as a whole. You typically do not unwind the old cassette onto itself.
A typical dual-line consumer head has two exit eyelets opposite each other and a spool with a divider or two channels. A single-line spool has one channel and one working tail. Arrows or “this way” molding on the spool or inner hub usually show wind direction. Stamped or molded numbers on the spool, hub, or head are the place to read the intended line diameter and, sometimes, whether the spool is single- or dual-line.
Why diameter and type matter
Use the diameter and general type the head or spool is marked to accept. Line that is too thick may not pass the eyelets, may stall the motor, or may stress the head. Line that is too thin may snap constantly, slip in the channels, or fail to trigger the feed mechanism. Shape—round, twisted, or serrated—is a preference only if the line still fits the eyelets and the marked size. No shape is universally better.
If there are no markings and no manual, do not guess a “standard” size. Compare the old line’s thickness to remaining pieces, check the manufacturer’s documentation for that model, or take the spool to a dealer who can match the head. Using leftover line of unknown size is a common reason a freshly strung head will not feed.
What you need
Prepare the consumable and a few simple tools before you open the head. You do not need a specialty kit for most consumer bump-feed heads.
- Replacement line that matches the diameter indicated on the head or spool, in a length sufficient to fill that spool without stacking above the flanges. The old line should be discarded if it is brittle, welded into a lump, badly flattened, or fused from heat.
- Eye protection and gloves.
- Scissors or line cutters to square the ends. Pliers can help pull a stubborn tail through an eyelet. A flat tool may help release plastic tabs; do not grind or force the housing.
- A pre-wound spool or cassette instead of bulk line when the old spool is damaged, the head is a drop-in unit, or you restring often and want to skip hand-winding. The replacement must be made for that exact head, not merely the same line size.
Keep small parts in order as they come off: cap, lock tabs, spring, washer, and inner spool. Photograph the stack or lay the parts out in sequence. Some heads are sold only as complete pre-wound units; if yours is one of those, bulk line on the old core is the wrong path.
Remove the cap and take out the spool
Most consumer bump-feed heads open by releasing a cover, lifting out the spool, and exposing a spring underneath. The exact latch is not universal. Typical patterns include squeezing opposing tabs, twisting a cover in the direction molded on the rim, or unscrewing a cap by hand. Support the head with one hand so the spring cannot fly out when the cover lets go.
Lift the spool straight off the hub. Note which face was outward and how any washer sat on the spring. If the line is still threaded through the eyelets, pull the tails inward or cut them so the spool can come free without bending the eyelets. Lay the parts in the order they came off.
Before you rewind, clean what you can see. Brush out grass, sand, and melted beads of old line from the eyelets, the bump mechanism, and the inside of the housing. Debris in an eyelet is a frequent cause of no-feed after a careful rewind. Do not soak plastic parts in harsh solvents unless the manual allows it; dry brushing is the conservative first step.
Stop and change the job if the head is cracked, the bump knob is seized, an eyelet is worn into a sharp groove, the spring is broken, or a lock tab is missing. Those are replacement-part problems. Do not pry violently, drill new holes, or modify the housing to make an ill-fitting spool stay put.
Rewind a typical dual-line bump-feed spool
This is the core hand-wind sequence for a generic dual-line, split-spool bump-feed head. Single-line spools, fixed-line pieces, and cassettes are follow-the-markings exceptions.
Find the wind direction
Look for arrows or wording molded into the spool or the inner hub. Wind in that direction on both sides. Winding against the arrows is a common reason the line binds or will not pay out when you bump the head. If one side of a dual spool has its own arrow, treat each channel independently and still keep both sides equally filled.
One piece through a center slot, or two equal pieces
Many dual-line spools use one length of line folded or pushed through a center slot so each half fills its own channel. Others use two separate pieces, one in each channel. The spool itself usually shows a slot, holes, or a divider that tells you which pattern it wants. Do not mix both lines in a single channel. Crossing the two lines, or letting one ride up over the divider, is a frequent cause of a head that will not feed.
If you are cutting line from a bulk coil, cut only as much as that spool can hold under the flanges. There is no universal length or wrap count that fits every head. Fill until the coils sit even and below the rim, then stop. Overfill is as harmful as too little line.
Wind firm and even
Hold the line under light tension so each turn lies next to the last, not in loose loops and not in overlapping ridges. Keep the coil below the spool flanges. Piled line above the rim will rub the housing, melt, or lock the spool so it cannot turn when you bump.
Leave two tails long enough to reach through the eyelets after the spool is back in the head, plus a little extra to grip. Many spools have temporary notches or clips on the rim; park each tail in its notch so the coil cannot spring loose while you handle the spool. Square the cut ends so they feed through the eyelets instead of mushrooming.
Seat the spool and thread the eyelets
Confirm the spring and any washer are back on the hub in the same order they came off. Set the wound spool onto the hub so it sits flat and can compress the spring. Release each tail from its parking notch and push it out through the matching eyelet—left tail through the left eyelet, right through the right, unless the head is clearly marked otherwise. Pull just enough line through so the tails cannot slip back inside when you fit the cap. The line should exit freely; if it scrapes, the eyelet may still hold debris or the line may be the wrong diameter.
If you wind the wrong way, cross the two lines, or fill past the flanges, expect the head to refuse to advance line even though it looks full. Unwind and correct those three errors before you close the head.
Install a pre-wound replacement spool instead
A matching pre-wound spool or cassette is often faster and reduces winding errors when it is the correct part. Confirm compatibility with that exact head: the hub shape, the location of the line exits, and the way the cap locks all have to match. Same line diameter on a different spool is not enough.
The usual drop-in sequence is:
- Orient the factory-wound spool so its line exits line up with the head’s eyelets.
- Route the tails through the eyelets.
- Set the spool onto the spring and washer in the original order.
- Compress the spring evenly and lock the cap until the tabs or threads are fully engaged.
Buying a pre-wound unit is the wiser path when the old spool is cracked or warped, you restring frequently and want a consistent wind, or the head is designed as a sealed cassette that is not meant to be refilled with bulk line. Do not force a “close enough” spool into a different hub. Compatibility is model- and head-specific; there is no universal drop-in spool.
Reassemble, set a working line length, and check feed
Return the parts in the reverse order they came off: spring, washer if present, wound spool with tails through the eyelets, then the cap. Press or twist the cap until it is fully locked. A cover that is only sitting on the rim can walk off when the head spins. Tug the tails gently to confirm they still slide, and turn the bump knob by hand if the design allows it, so you can feel that the spool is free to move a little against the spring.
How much line should stick out
Leave only a short working length of line outside the eyelets. There is no single correct measurement that fits every shield and head. Many debris shields include a line-limiter knife—a small blade on the guard that trims excess after startup if the shield is correctly installed. If your guard has that knife, install the shield before any test run and let it cut the line to the designed radius. If there is no knife, follow the length shown in the model instructions, or leave only enough line to cut without slapping the shaft or the guard.
Do not run the head as a test fixture with the guard off. Restart only after full reassembly and the normal starting procedure for that power type: battery reinstalled, cord plugged in, or gas model started as the manual describes. Keep people and pets clear of the cutting radius.
How feed is supposed to work
On a bump-feed head, line typically advances when the bump knob is tapped on the ground with the head already spinning. A light tap is the intended motion; grinding the knob into dirt is not. Auto-feed heads advance by a different internal mechanism. Do not assume bumping an auto-feed head will work the same way, and do not disassemble a sealed auto-feed unit to “help” it.
On a brief, controlled test, look for line exiting both sides on a dual-line head, a cap that stays closed, and no unusual vibration that would suggest a loose cover or an unbalanced, half-empty spool that has jumped its hub. Stop immediately if the head opens, the tool shakes hard, or you smell melting plastic.
If the line will not feed or keep breaking
Most post-restringing problems are mechanical mistakes in the head, not engine or motor faults. Work through the cutting end before you look elsewhere.
- No feed after a bump or auto-feed cycle: Overfill, winding against the arrows, and crossed lines on a dual-line spool are the ordinary causes. Open the head and check that each line sits in its own channel, below the flanges, in the marked direction. Also check that the spring is present and seated; a missing spring leaves the spool unable to index.
- Line that snaps as soon as it cuts: Wrong diameter, old brittle line, and sharp or grooved eyelets all nick the line as it exits. Replace worn eyelets or the head if the metal or plastic has a cutting edge. Fresh line of the marked size is the conservative consumable fix; do not step up to a thicker line to “make it last.”
- Bump knob that does not click, or a cap that walks off: Inspect lock tabs, threads, and the knob for cracks or packed debris. A cap that is not fully locked will unscrew in use. Do not tape or wire a loose cover in place.
- Melted line inside the housing: Rubbing from overfill, sand in the eyelets, or a spool that cannot turn will heat the line until it welds into a lump. Clean the head and rewind below the rim. Repeated melting after a correct rewind can mean the head itself is worn and needs replacement rather than another coil of line.
Cleaning eyelets and correcting the wind fixes many no-feed heads, but not every one. Stop and use the manufacturer’s instructions or a qualified shop if you find fuel leaks, electrical faults, a bent shaft, a shattered head, or a tool that will not isolate from power. Those are outside restringing.
Limits of a generic restringing guide
Some heads never take bulk line on the old spool. Fixed-line designs need preformed pieces. Cassette heads need the matching cartridge. A few consumer units use a one-way winding window in the assembled head; those still follow the arrows on that head, not a dual-channel rewind on the bench. If what you see does not match a cap, spring, and marked dual-line spool, do not force this sequence.
Owner’s markings and the model manual always override a generic article. Diameter, capacity, cap direction, and whether the spool is single- or dual-line are head-specific. A sequence that works on a typical bump-feed dual-line head can bind an auto-feed or proprietary cassette.
Do not modify the head to accept thicker line, remove the debris shield, or defeat lockouts so the tool will run with the cover off. Forcing oversized line or running without the guard increases the risk of injury and works against the way the tool was built to be used. When the head is damaged or clearly not the generic pattern described here, get the correct replacement part or manufacturer support instead of inventing a workaround.
Restringing restores cutting line. It does not promise that the trimmer will cut like new, that one wind will last a season, or that every head on the market will accept the same method. Identify the head, isolate the power, load line the way that head is marked to take it, and close the assembly so the line can feed. That is the whole job.
