Reloading a strimmer means putting fresh nylon cutting line into the cutting head so the machine will cut again. On most consumer petrol, mains-electric and battery models you either fit a new pre-wound spool or cassette, or rewind line onto the existing spool, then feed the ends through the eyelets and refit the cover. Match the line size marked on the head or in the manual, and follow the wind arrows on the spool, because head designs differ.

What reloading a strimmer actually involves

A strimmer, also called a string trimmer or grass trimmer, cuts with spinning nylon line rather than a metal blade. When that line is used up, broken off, or welded into a lump inside the head, the machine will still run but it will not cut. Reloading restores the consumable: the nylon cutting line, also sold as trimmer line.

On typical home machines there are two common paths. One is to buy a pre-wound spool or cassette that already has line on it, lift out the empty one, and drop the new one in. The other is to buy a coil of loose line and rewind it onto the reusable spool that came with the head. A smaller group of heads does neither: they take short pre-cut lengths pushed into slots or holes. Those fixed-line heads are reloaded by replacing the stubs, not by winding a drum of line.

How the line then pays out depends on the head type:

  • A bump-feed or tap-and-go head holds spare line on a spring-loaded spool. With the head spinning, a tap on the ground releases a short extra length through the eyelets.
  • An auto-feed head also stores line on a spool, but a mechanism inside pays line out without a tap. The internals vary by maker, so treat the markings on your head as the guide rather than assuming one brand’s clutch or sensor.
  • A fixed-line head has no winding spool. You insert short pieces and replace them when they wear down.

There is no single sequence that fits every brand. Caps unclip, unscrew or twist in different ways. Some dual-line spools have a divider and two channels; others use one length folded in half. Some retaining nuts undo opposite to the way you first try. The markings moulded into the cutting head, the arrows on the spool, and the model instructions decide the path. Use this article to recognise which method you have and to work safely; do not force a generic teardown onto a head that is clearly built differently.

Safety before you open the cutting head

The cutting head is meant to spin at high speed. Line, grit and broken stubs can fly when you test it. Isolate power before you touch the head, and keep the guard on whenever the machine is started.

Isolate the power source

  • Battery strimmer: remove the battery pack and keep it away from the tool until the head is fully back together.
  • Mains-electric strimmer: unplug the lead from the socket. Do not rely on a switch alone.
  • Petrol strimmer: wait until the cutting head has stopped, then disconnect the spark-plug cap so the engine cannot start while your hands are on the head.

Wait until every moving part has stopped. If the machine has just been used, a petrol engine, silencer and gearbox can be hot enough to burn. Give them time to cool before you rest the tool on your lap or work close to the engine. Keep fuel and exhaust away from sparks and from anything that can catch. Work where children and pets cannot reach the tool or the loose line.

Protect your eyes and keep the guard on

Wear eye protection when you later test the head. Nylon line can whip, and debris left in the grass can be thrown. Gloves help when you are pulling old, sharp stubs out of eyelets. Follow any extra protection listed on the machine label or in the model manual. Do not remove the cutting guard to “see the line better” while the machine is running, and do not defeat interlocks. An unguarded head is not a safe test setup.

If the housing around an electric motor is cracked, or you can see damaged cable, stop and have the machine checked rather than opening electrical enclosures yourself.

Identify the head, the spool and the eyelets

Look at the cutting head before you prise anything apart. Most consumer bump-feed and auto-feed heads have a removable cover over a plastic spool. Around the rim you should see one or two metal or plastic eyelets: these are the exit holes the line must pass through. Dual-line heads have two eyelets opposite each other. Single-line heads have one. Fixed-line heads look different: short stubs of line stick out of slots or holes, and there is no drum of spare line inside.

Opening a typical bump-feed cap

Many covers unclip with tabs you squeeze, or unscrew by hand. Support the head so you are not twisting the shaft. Press the tabs evenly rather than levering one side with a screwdriver, which can snap thin plastic. If the cover is a screw type, note which way it loosens before you apply force. Some retaining nuts do not undo in the direction you expect; if the nut will not move with firm hand pressure, check the manual or the moulded arrows instead of using grips that round the flats.

Under the cover you will usually find a spool, sometimes a spring, and sometimes a washer or drive dog. Lay the parts out in the order they came off. The spring is easy to lose and the head will not feed properly if it is left out or put back upside down. Photograph the stack with your phone if the arrangement is not obvious.

Spool clues: dual line, slots and arrows

A dual-line spool often has a centre divider or two separate channels. You may see small slots or hooks on the rim where the midpoint or the ends of the line are parked while you wind. Many spools have arrows or a “wind this way” moulding. Those arrows matter later: winding against them is a common reason the line will not pay out when you bump the head.

If the housing is already cracked, an eyelet is torn out, or the nut is rounded off, stop. Forcing a damaged head is more likely to leave you with flying fragments than with a working trimmer. Replacement heads are consumable parts; a dealer or the model parts list is the safer next step.

Choose line that matches the head

The correct line diameter is the one printed on the cutting head, on the old spool, or in the model instructions. That marking is the one that matters. Do not assume a size just because it is common in garden centres.

Line that is too thick can jam in the eyelets, refuse to feed, or stress the plastic spool and cover. Line that is too thin may break as soon as it hits anything, or it may slip and feed poorly. If the old stubs are still in the head, you can compare them by eye to a new coil, but still confirm against the printed specification rather than guessing.

Shape, length and storage

Consumer trimmer line is sold in several shapes: round, twisted, and various edged or multi-sided profiles. Shape is a practical choice, not a ranking. Round line is widely available and tends to wear in a predictable way. Twisted and edged lines are often chosen because they can feel more aggressive on thick grass or because some users find they whistle less. Wear rate and cut quality still depend on what you are cutting, how you hold the head, and whether the line diameter is correct. There is no reliable way, from a general article, to say one shape always lasts longer or uses less battery or fuel.

Buy a length that will fill your spool without bulging past the flanges. The spool itself is the capacity guide. Overfilling is a frequent cause of no-feed after a careful rewind. Keep unused line in a cool, dry place out of strong sunlight. Old line that has sat in a shed for years can go brittle and snap at the eyelet. Some people soak line in water hoping to soften it; that is not a reliable or universally safe treatment for every nylon blend, so treat it as optional folklore rather than a required step.

Method 1: fit a pre-wound spool or cassette

A pre-wound spool is the simpler reload if your head was designed to take a matching cassette. “Matching” means the same style of spool that came out of your head, not any cassette that looks roughly the same diameter. Brands are not interchangeable just because both are dual-line plastic drums.

  1. Isolate power as described above and wait for the head to stop.
  2. Open the cover and lift out the old spool. Pull any remaining line stubs out of the eyelets so nothing is trapped in the holes.
  3. Note the spring, washer or drive pieces. They stay with the head, not with the discarded spool, unless the new cassette is sold as a complete cartridge that replaces that stack. Refit them in the same order and orientation you found.
  4. Seat the new spool so each factory-cut end can reach an eyelet. On a dual-line head that usually means one end through each opposite hole.
  5. Thread the ends through the eyelets before you close the cover, unless the cassette instructions show a different parking slot. Leave enough tail outside that the line cannot slip back inside when the cover goes on.
  6. Align any tabs, slots or marks on the cover with the body and lock it fully. A cover that is only half on will either fly off or pinch the line so it cannot feed.
  7. Check that no loop of line is trapped under the rim, that the spring is still in place if the head uses one, and that the guard is fitted. Only then restore the battery, plug or spark-plug cap.

There is no universal click count, twist angle or torque figure for the cap. Hand-tight and fully seated is the aim. If the new spool will not drop in without force, you likely have the wrong cassette or a piece of the old stack still inside.

Method 2: rewind line onto the existing spool

Rewinding is the usual DIY route when you have a bump-feed or many auto-feed heads and a coil of loose line. Work on a clean bench so grit does not go back into the head.

Prepare the spool and cut a manageable length

Remove the old line completely, including scraps jammed in the eyelets. If two old ends have melted together, cut the lump away rather than trying to unwind a welded mass. Check the spool for cracks and for worn hooks or a damaged divider. A cracked spool should be replaced, not rewound.

Cut a length that will fill the spool without standing proud of the flanges. The right amount is “enough to wind neatly to the capacity of this spool,” not a single number of metres for every machine. If you overshoot, unwind a little and trim. It is better to underfill slightly than to pack the drum so tight the cover will not close or the line cannot move.

One length or two, and which way to wind

Dual-line heads often take either two equal lengths, one in each channel, or one longer length folded at the midpoint and hooked into a centre slot. Look at the spool: a hook or notch in the middle usually means fold and hook; two separate start holes usually mean two pieces. Single-line heads take one length started in the single anchor hole.

Wind in the direction of the moulded arrows. Those arrows are there because the bump or auto-feed mechanism pays line out one way. Winding against them, or winding the two channels in opposite directions when they should match, is a frequent cause of a head that looks full but will not release line. Keep each turn neat and firm against the last, without overlapping in a heap and without hauling so tight that the line bites into itself and binds. On a divided spool, keep each line in its own channel.

Tails, eyelets and how full is full

Most spools have small notches on the outer rim where you can park a short tail so the winding does not spring undone while you carry the spool back to the head. Leave enough tail to pass through each eyelet with a few centimetres to spare once the spool is seated. Some designs want you to thread the eyelets after the spool is in the housing; others want the tails already pointing at the holes. Either way, the finished job has one clean end coming out of each eyelet, not a loop trapped under the cover.

Stop winding when the line sits level with or just below the spool flanges. A bulge will rub the cover, generate heat, and can weld the nylon into a solid ring the first time you use the machine hard.

Neat winding reduces tangles. It does not guarantee the line will never snarl. Grass sap, a missing spring, or a cover that is not fully locked can still stop the feed.

Reassemble, restore power and check that line feeds

Drop the wound spool into the housing in the same orientation it came out, usually with the arrows or the labelled face visible as they were. Refit the spring if the head has one. Guide each tail through its eyelet. Equalise the two ends on a dual-line head so the head is not lopsided. Fit the cover so every tab or thread is engaged. Turn the spool by hand if the design allows: the line should be able to move a little, not sit locked solid.

Confirm the cutting guard is in place. Restore power only after the head is closed: battery in, mains plug in, or spark-plug cap back on. The first run should be outdoors, on a clear patch of ground, away from people, glass, vehicles and loose stones.

How feed is supposed to work

On a bump-feed or tap-and-go head, bring the spinning head down so the button in the centre taps the ground. A short extra length should appear through the eyelets. Do not hammer the head; a controlled tap is enough. If the machine has a cut-off blade on the guard, extra line will be trimmed to length automatically. On an auto-feed head, the mechanism should pay out line without a tap once the head is up to speed and the remaining tips are short. You do not need to understand a particular clutch to use it; you only need to see whether line appears.

A short test is enough. If nothing comes out after a couple of taps, or the auto-feed does not release anything, stop, isolate power again, and reopen the head. Do not keep running a head that is clearly jammed: that is how line welds and how plastic overheats. This article does not cover petrol starting rituals, choke settings or battery diagnostics; if the engine or motor will not run at all, that is a different problem from reloading.

If the line will not feed, keeps breaking or welds in the head

When a reload fails, the cause is usually mechanical and visible once you open the head again.

  • Windings that overlap, cross channels, or were wound against the arrows will not pay out.
  • The spool is overfilled, so the cover pinches the line.
  • The line diameter is thicker than the eyelets or the head marking allow.
  • The spring was left out, inverted, or crushed.
  • The cover is not fully locked, so the spool cannot turn, or it is locked on top of a trapped loop.
  • Old, brittle line snaps at the eyelet as soon as it hits a fence or dry stalk.
  • Worn eyelets have developed a sharp groove that cuts new line.
  • Too little line was showing when the head was last used hard, so friction heated the remaining nylon and welded it into a lump.

Cut welded line out and rewind, or fit a new spool. Replace a spool or head whose eyelets are knife-sharp or whose housing is cracked. Fresh line of the specified diameter, wound neatly in the marked direction, solves most feed faults. Heat-welded line after a long session with almost no tips showing is a reason to stop earlier next time and tap or allow auto-feed before the tips disappear completely.

If the machine itself will not start, the shaft does not turn the head, or there is an obvious clutch or gearbox problem, reloading the line will not fix it. Do not open motor housings or sealed gearboxes to investigate. Those jobs belong with a dealer or a competent repairer.

When to replace the head or stop and get help

Stop using the machine and replace the head, or take it to a dealer, if you can see any of the following:

  • A cracked or split housing that can throw fragments.
  • Destroyed or missing eyelets.
  • A rounded, stripped or cross-threaded retaining nut.
  • A missing or broken cutting guard.
  • A fixed-line or specialist head whose slots are worn so they no longer grip pre-cut lengths.

Consumable cutting heads are often cheaper and safer than fighting a damaged one with improvised fasteners. Electric motor housings and sealed gearboxes should stay closed. A cracked motor case, damaged mains cable, or a petrol machine with a fuel leak is a stop point, not a DIY rewind job.

If you cannot identify whether you have a bump-feed, auto-feed or fixed-line head, or the retaining parts do not match any of the patterns above, follow the model manual or ask a dealer with the model number in hand. The markings on the tool take precedence over any generic how-to, including this one.

Quick recap

  • Reloading restores nylon cutting line so the strimmer can cut again.
  • Most consumer heads take a pre-wound spool or loose line wound onto the existing spool; some take short fixed lengths instead.
  • Remove the battery, unplug a mains machine, or disconnect the spark-plug cap on a petrol model before you open the head.
  • Use the line diameter marked on the head, spool or in the instructions.
  • Follow the wind arrows, keep windings neat, thread the eyelets, and lock the cover with every spring and washer back as found.
  • Test outdoors with the guard on. Tap a bump-feed head to release line; stop and reopen the head if nothing feeds.
  • A cracked head, ruined eyelets or a missing guard means replace the head rather than keep using it.