Why Your Spool Keeps Jamming

A spool that keeps jamming isn’t bad luck — it’s almost always one of five specific causes, and each has a clear fix. If you’re re-opening the head every few minutes, work through these and you’ll usually cure it for good.

1. Heat welding

The most common cause. Friction and engine heat soften nylon, and loosely-wound coils fuse together so they can’t pay out. Prevention: wind tight and flat (see How to Wind a Trimmer Spool), and don’t run the spool down to the last few feet, where heat is concentrated.

2. Wrong line gauge

Line thicker than the head’s rating binds in the eyelet every single time. Prevention: match the gauge your head is built for — details in Choosing Trimmer Line Gauge.

3. Cross-winding

If coils overlap or criss-cross instead of lying in even rows, the line snags itself the moment it tries to feed. Prevention: wind in tidy layers in the arrow direction; on dual-line spools, keep the two strings in their separate channels.

4. Cheap or brittle line

Low-grade nylon, or any line stored in sunlight, goes brittle and snaps off inside the head — leaving a stub that won’t feed. Prevention: buy quality line and store spools out of UV. Twisted line frays less than round (see Twisted vs Round vs Serrated).

5. A worn head

A grooved or sharp eyelet, or a weak/displaced feed spring, will fight you no matter how perfectly you wind. Prevention: inspect the eyelet and spring when you swap spools; if the eyelet’s worn through, it’s time for a new head — possibly a tougher universal one.

When it’s none of the above

If you’ve addressed all five and a correctly wound spool of the right gauge still jams, the spool itself may be a poor match for your head. Verify the exact part for your model — start from How to Measure Your Old Spool and confirm fitment on the Brands page. For a live walk-through of the symptom, see the troubleshooting checklist.