A cautious troubleshooting path
Why does my string trimmer line keep breaking?
Repeated breakage is frustrating, and owners often ask whether tougher or thicker string will help. First locate where it fails. A symptom is not approval to upsize.
Where does the line break?
At the exposed end after striking hard ground or edging
Line is a wear part and can break when it contacts pavement, curbs, stone, or other hard surfaces. Greenworks’ US support guidance says line breaks more often in harsh terrain or when edging; it points owners to keep the head/guard area clean and the cutting blade clear and sharp. That guidance is specific to its support context, not a universal diagnosis.
At the eyelet or inside the spool head
Do not assume the diameter is the cause. Verify the line type and size against the exact model/head manual, then check that the winding pattern and threading steps match that head’s instructions. A damaged eyelet, spool, or head requires the manual’s service path or an authorized repair center.
The line will not feed or the head jams
Stop using the machine. Use the exact head’s manual for reloading and debris removal. Check whether the installed head is approved for the model, and whether the line size/profile is listed for that head. Do not force-feed or install a larger diameter as a test.
Before buying a different size
- Record the full model and SKU from the tool label.
- Identify the installed cutting head; it could have been changed after purchase.
- Find the manual for that model revision and region.
- Verify line diameter, shape/material, and loading directions for that head.
- Compare the failure point and cutting conditions with the manual’s troubleshooting section.
- If the head is damaged, parts are missing, or the cause remains unclear, contact the maker or an authorized service provider.
Why thicker line may make things worse
Line with a larger diameter can add load and may exceed the motor, spool, eyelet, or guard design. Manufacturer limits are not interchangeable between models, and a head sold separately can have different requirements than the factory head. Never choose the largest size simply because line wears quickly.
Source-grounded facts
The US Greenworks ST60L413 support page says line can break more often on harsh terrain or when edging and advises keeping the underside of the head/guard area clean and the cutting blade clear and sharp. EGO’s ST1520 manual lists heavy line as one possible reason the trimmer stops while cutting and directs use of nylon line no greater than 0.095 inch (2.4 mm) for that model. These are model-specific examples, not general troubleshooting rules for all machines.
Common questions
Will a thicker trimmer line last longer?
It may not. Contact, line profile, winding, and head condition matter. Use a larger diameter only if the manual for your exact model and head allows it.
Does line breaking at the tip mean the line is too thin?
No single diagnosis follows from that symptom. Frequent contact with hard surfaces can consume line; line that breaks at the eyelet suggests a different inspection path. Follow the manufacturer instructions rather than changing diameter by trial.
Can I use metal line for tougher weeds?
Only use materials the exact manual approves. Some homeowner trimmer manuals specifically forbid metal or reinforced line. This checker does not recommend wire.
Community posts in the project research surfaced recurring breakage and “should I go thicker?” questions. These are qualitative examples, not prevalence data. Manufacturer links and the current evidence date are on the source index.