Restringing a trimmer means making the tool safe, opening a serviceable cutting head, clearing old line, cutting compatible new line, winding it evenly in the direction marked on the spool or head, seating the ends through the eyelets, reassembling, and confirming the line feeds. Head type, line diameter, length, and wind direction vary by model, so follow the markings on your head or the owner’s manual rather than treating one procedure as universal.
What restringing a trimmer actually means
Restringing reloads a user-serviceable spool inside a string trimmer head so the tool can feed trimmer line again. The nylon (or similar) line is the cutting element. When it is too short, fused, or gone, the head may spin without cutting, or it may refuse to advance line when you bump or trigger a feed.
That is different from installing a pre-wound spool. A pre-wound replacement arrives already filled. You still make the tool safe, open the head, and seat the ends through the eyelets, but you skip measuring and winding bulk line. Neither option is automatically cheaper, faster, or more reliable. Bulk line is convenient if you already have the correct diameter. A matching pre-wound spool is simpler if the winding pattern is unclear or the old spool is damaged.
It is also different from a fixed-line head, which holds short pre-cut pieces in slots or clamps instead of a long wound coil. Reloading those heads is inserting new segments, not winding a spool.
Restringing is the right job when the head is intact, the spool still turns, and the design is meant to be refilled by the owner. It is the wrong job when the housing is cracked, a spring or retainer is missing, the eyelets are badly grooved, or the head is a sealed or proprietary cassette. Then a replacement spool or a new trimmer head is the safer path.
This article covers the shared sequence on many consumer bump-feed and similar spool heads: lock out power, identify the head, choose compatible line, open the retainer cap, clear old line, wind in the marked direction, reassemble, and test feed. You still must verify on your own machine whether the spool is single-line or dual-line, the stamped line diameter, how much line the spool can hold, which way the winding arrow points, and whether the head is a quick-load design that should not be fully torn down. If those details are missing, stop and check the manual rather than guessing.
Make the trimmer safe before you touch the head
Do not open a trimmer head while the tool can still start or while the cutting assembly is still moving. The lockout hardware differs by power type, but the rule is the same.
On a corded electric string trimmer, unplug the cord from the outlet and from the tool if it disconnects at the handle. Do not rely on the trigger alone. On a battery model, remove the battery pack and set it aside. On a gas model, switch the engine off, keep your hands off the starter, and wait until the cutting head has fully stopped. Gas engines and exhaust can stay hot after shutdown. Let the unit cool before you kneel beside the head or rest the shaft across your legs. Some models add interlocks or a shaft lock used when the cap is turned. Follow those steps if your manual describes them.
Wear eye protection, and consider a face shield for the later feed test. Line and debris can be thrown at high speed. Keep fingers out of the cutting path and away from the eyelets while anything can still move. Gloves help when you pull fused or sharp-ended line, but they do not replace waiting until the head is still. Never defeat a guard, and never work on a running engine or a spinning head.
If you must tip a gas unit to reach the head, do it only after the engine is off and cool, and watch for fuel movement. Tipping a fueled trimmer can spill gasoline. Keep the tank as upright as you can, work in a ventilated area, wipe any spill before you continue, and keep ignition sources away. Set the trimmer on a stable surface, clear children and pets from the area, and use a small tray for the retainer cap, spring, and washers so parts do not disappear in the grass.
Identify the head type and whether you can restring it
Consumer heads do not all load the same way. Matching the method to the design keeps you from forcing a teardown the head was never meant to receive.
A bump-feed head is the usual user-serviceable pattern. Line is stored on an internal spool. Tapping the knob on the ground while the head spins releases a short length. These heads typically have a removable retainer cap, a spool, often a spring, and one or two eyelets where line exits.
An auto-feed head also stores line on a spool, but it advances line without a deliberate bump, often by metering as the line wears. The outside can look like a bump-feed head. For restringing, what matters is whether you can open it and whether the spool shows a wind direction.
A quick-load head lets you pass a measured length of line through the housing—often in one eyelet and out the other—then wind by turning a knob or the outer housing. You may not need to lift the spool out. If you see a through-path and a winding knob, do not assume you must dismantle it like a traditional bump-feed spool.
A fixed-line head uses short pre-cut pieces rather than a wound coil. You insert each piece into a slot, hole, or clamp until it locks. There is no winding arrow and no dual-line channel to fill. Spool-style restringing does not apply.
Before you open anything, look at the cap, the spool if it is visible, and the housing for:
- A winding arrow or wording that shows wind direction
- A stamped line diameter or size range
- Release tabs, a cap-turn arrow, or a release slot
- One eyelet versus two
A single-line spool feeds one strand. A dual-line spool feeds two strands, usually through opposite eyelets, and often has a divider or two channels so the lines do not nest. Two eyelets often mean dual-line use, but confirm on the spool rather than assuming.
If there is no cap release, no spool access, and no through-load path, the head may not be user-serviceable with bulk line. Sealed heads and some proprietary cassettes are meant to be replaced as an assembly. Do not pry them apart to improvise a wind.
Choose compatible line and a workable length
The correct line diameter is the one specified for your head, not a generic size. Check a stamp on the trimmer head or spool first, then leftover packaging if you know it came from this machine, then the owner’s manual. That marked size is the main compatibility rule.
Oversized line can jam in the eyelets, stop the spool from turning, or keep the cap from sitting flush. Undersized line can slip, weld under heat, or break as soon as it hits grass or a hard edge. If the head lists a range, stay inside it. Do not upsize for toughness unless the manual allows it.
Length is also model-specific. Do not fill by a universal footage. Use the capacity cues on the spool: a fill line, the height of a divider, rim slots that only work when the coil stays below the edge, or a maximum length in your manual. Overfilling is a common reason a freshly wound head will not feed. The coil needs room to turn and release line without binding on the housing.
On a dual-line spool, keep the two lengths equal when the design uses two strands of the same reach. Uneven coils let one side bind while the other runs out. Some heads use one long piece folded in the middle and seated in a center notch, with each half wound into its own channel. Use that pattern only if your spool has a marked center slot or the manual describes it.
Line shape and material can change stiffness and how the coil sits, but they do not replace diameter and length. Stay with the size the head calls for and wind neatly. Do not assume a shaped line will last longer or cut better in every condition. Cut new line with a sharp cutter so the ends thread cleanly. If length is uncertain, a conservative amount below the fill cues is safer than packing the drum and forcing the cap on.
Open the head and clear the old line
With power removed and the head still, hold the housing so it cannot spin. Many bump-feed caps unscrew, sometimes after you press tabs. Others lift off when tabs are squeezed. A few have a slot that accepts a screwdriver or an accessory only to release a lock, not to pry the plastic apart. Follow the cap markings. If it will not move, look again for hidden tabs instead of forcing it.
When the retainer cap comes off, the spool usually lifts straight out. Expect a spring under the bump knob or between the spool and the housing. That spring can launch. Keep a thumb over the assembly as it separates and put the spring in your tray immediately. Note the spool orientation, any washers, and which face pointed outward. A photo of the stack on your own phone can help you reverse the order later; it is not a substitute for the manual.
Pull out all old line. Discard line that is fused into a lump, brittle enough to crack when flexed, deeply notched, or tangled into crossed layers. Winding over a fused pancake is a reliable way to stop feed.
Inspect before you rewind:
- Eyelets present and not worn into sharp grooves that will fray new line
- Spool turning on its post without a flat spot or melted skirt
- Spring intact and not collapsed
- Housing and retainer cap free of cracks
- Bump knob, if present, moving as the design intends
Brush out grass, packed dirt, and melted nylon crumbs. Grit between the spool and housing acts like a brake. If the housing is cracked, an eyelet is missing, or a part has nowhere to go, stop. A missing spring or broken retainer is a reason to replace parts or the whole head, not a reason to assemble close enough.
Cut, wind, and seat the new line
Winding direction is not a preference. Follow the winding arrow or “this way” mark on the spool or head. Winding against the arrow is a frequent cause of a head that looks full but will not advance. If there is no arrow, check the manual. Do not invent a direction from a messy leftover coil.
For a traditional removable spool:
- Cut compatible line to a length that stays within the spool’s capacity cues. For dual-line designs that use two equal strands, cut two matching pieces, or one longer piece only if the spool is clearly meant to be folded in the center.
- Anchor the line in the hole, slot, or center notch the spool provides so the first turn cannot slip.
- Wind tightly and evenly in neat layers. Do not crisscross the line in a way that locks the coil.
- On a dual-line spool, keep each strand in its own channel or on its own half of the divider. Do not let the two lines nest into one pile.
- Stop while the coil is still below the rim or fill mark. Leave enough free end to pass through the housing eyelets. If the spool has temporary holding slots on the rim, park the ends there so the coil does not unwind while you drop the spool into the head.
Keep light tension as you wind so the coil does not spring loose. If a layer climbs the wall or overlaps the divider, unwind a few turns and lay it down again. A slightly shorter, even coil feeds more reliably than a stuffed, crossed one. There is no universal turn count or leftover eyelet length; those change with spool size and line diameter.
Quick-load heads use a different sequence. You typically align the housing so a through-path is open, push a measured length in one eyelet and out the other until the ends are roughly even, then rotate the knob or housing in the marked direction to draw the line inside. Match that design instead of pulling the spool out and rewinding it like a bump-feed drum. Forcing a teardown can lose small parts or break the through-path.
Fixed-line heads take pre-cut segments. Insert each piece to the depth or click the design requires, and keep both sides matched if the head cuts with two exposed ends.
Reassemble the head and confirm the line feeds
Route the free ends through the housing eyelets before you close the head. On a typical dual-line head that means one end through each opposite eyelet. Pull them through so they cannot slip back inside. If you used temporary rim slots, release the ends from those slots as you feed them through the eyelets, then let the coil sit in the housing.
Reinstall the spring in the orientation you found. Set the spool on its post so it sits flat and can rotate. Align any tabs, keys, or notches with the matching features in the housing. Put the retainer cap on and turn or snap it until it is fully seated. The cap should sit flush and should not rattle. If it will not close, do not force it. Check for an overfilled coil, line trapped under the cap, a spring out of its pocket, or a spool that is upside down.
Trim the exposed ends only enough that they will not whip into the guard in a wild loop. Many guards include a line-limit blade that shortens excess after the head is spinning. You do not need a precise pre-cut working length if that blade is present and in good condition, but the ends must be long enough to feed.
Restore power only after the head is fully closed and the guard is in place. Work in a clear area away from people, glass, and vehicles, and wear eye protection. Plug in a corded unit, reinstall a battery, or start a gas unit only after it is upright, the cap is tight, and there is no spilled fuel.
Use the head’s normal feed method. On a bump-feed head, that is typically a light tap of the bump knob on bare soil while the head is up to speed—not a slam on concrete. On an auto-feed head, run the tool briefly and see whether line meters out. On a quick-load head, confirm both ends are present and the winding knob did not back off.
A successful feed looks like this: the head spins without rubbing, line extends from the eyelet or eyelets, a bump or auto-feed produces a short additional length rather than dumping the whole coil, and the guard’s limit blade (if equipped) trims obvious excess. If the head chatters, the cap walks off, or no line appears, shut the tool down, remove power, and troubleshoot instead of repeating bumps.
Why new line will not feed or breaks immediately
Most failures after a restring are mechanical.
The spool may be wound against the winding arrow, so the mechanism tightens the coil instead of releasing it. The spool may be overfilled and unable to rotate. Dual lines may be crossed or nested, locking both strands. The line diameter may be wrong for the eyelets. The ends may never have been passed through the eyelets, so the head is closed on a coil with no exit. The spring may be missing, upside down, or unseated. The retainer cap may be only partly snapped or threaded, so the spool floats and binds.
Line that snaps at the eyelet often rubs a sharp groove, or it was nicked when a stiff end was forced through a misaligned hole. Line that welds into a lump has usually been spinning without paying out, so friction heat melted it. Old brittle line can shatter on the first contact with a fence, sidewalk edge, or dry stalk. Fused residue left on the spool creates a high spot that scuffs every new layer.
If line feeds on one side only, check a dual-line divider that was overfilled on one half, or an end that slipped back through one eyelet. If the bump knob feels dead, check the spring and whether the cap is fully locked. If the head will not spin smoothly, look for line trapped between the spool and housing, a warped spool, or a rubbing cap.
Stop treating it as a winding problem when the hardware is worn out. A cracked housing, a missing eyelet, a spool with a melted core, a bent shaft, or a design that requires a proprietary cassette will not be fixed by neater coils. Replace the damaged part or the head, using the manual to identify the correct service piece. Do not keep bumping a head that is coming apart. Fresh line can also fail if you test against abrasive surfaces or operate with the guard removed. The guard controls debris and, on many units, trims extra line. Running without it is unsafe and can make line length look wrong when the real issue is an uncontrolled whip.
When to use a pre-wound spool or replace the head
A pre-wound spool is a reasonable alternative when you do not want to wind bulk line, when the original spool is chipped or melted, or when the winding pattern is hard to read and a matching cassette is sold for that head. You still lock out power, open the retainer cap, confirm the spring, thread the ends through the eyelets, and close the head. Fit is not guaranteed for every aftermarket spool. Match the head type and the stated line size, and compare the spool shape, bump interface, and divider to what you removed.
Replace the trimmer head, or have it serviced, when the housing is cracked, the eyelets are deeply cut, the bump mechanism is broken, internal parts are missing, or the unit uses a sealed or proprietary head that is not meant to be refilled with bulk line. Replace rather than guess when winding marks are absent and no manual is available. Forcing line into a damaged head can throw pieces or leave a tool that will not cut.
Go back to the owner’s manual for unusual lock tabs, a shaft that must be held a specific way to unscrew the head, a stated maximum line length, a required fold-in-the-middle notch, a quick-load length mark, gas-unit fuel and starting procedures, and any electrical interlock. Those instructions are specific for a reason. The sequence in this article covers a typical user-serviceable spool head; it does not replace the markings on your own trimmer. If the shaft, clutch, or motor is damaged, restringing will not restore cutting, and a qualified repair technician is the safer next step.
