How to Load and Replace String Trimmer Line (Any Head Type)

Running out of line while trimming is bad enough, but the worst part of using a trimmer is re-loading the line. Wrapping it up in reverse, over filling the spool, or choosing the wrong size line that gets stuck. All of this could be prevented by explaining the different types of trimmer heads that are available in about 2 minutes.

Step-by-step: Reloading a String Trimmer

1. Identify your head type. Bump-feed (most common): tap the head on the ground and it feeds more line from an internal spool. Fixed-line: no spool — you insert short pre-cut lengths (usually ~10–12″). Auto-feed: advances line automatically. Which one you have decides how you reload.
2. Choose the best line for the task at hand. Check that the line is the correct diameter for your model and ensure that you have the correct type of line for the job. Light grass is best attacked with round line but tougher weeds require the power of twisted/serrated line. Incorrectly sized line is the major cause of line jams.
3. Load a bump/auto-feed spool. This piece of leader is approximately 20–25 feet long. This leader will be threaded down into the anchor of the spool. The leader will then be wrapped around the core of the spool in tight and even fashion going in the direction of the arrows on the spool. If leader is wrapped in reverse fashion the auto-feed will not work. There will be 3–4 inches of leader protruding from the eyelets of the spool after leader has been wrapped around core. Now the bump spool can be put back together.
4. Load a fixed head. Simply feed a pre-cut length (~18″ total, ~10–12″ per side) through the head until it’s even on both sides — the easiest type to restring.
5. Unblock lines and prevent jamming. Lines get jammed between spools (when they are overfilled or unevenly wound) or because the wrong size line has been put on a reel. Lines also get hot and get jammed when they don’t feed off the reel properly. To prevent lines from getting jammed, wind your spools evenly and don’t put too much line on them. Should the line weld itself together inside the reel’s head, dismantle the head, feed the line back in neatly and reassemble the head.

Safety tip: power off and remove the battery (or disconnect the spark-plug wire on gas models) before touching the head.

Pro Tips

• Wind tight and even in the arrow direction — loose or reverse winding is the number-one reason auto/bump feeds fail.
• Don’t overfill the spool — it increases friction and jams.
• Keep a pre-wound spare spool (or a fixed-line pack) in your pocket for instant swaps.

Common Problems & Fixes

• Won’t feed line → wound against the arrows or overfilled. Rewind correctly.
• Line welded/fused together → heat from not feeding. Open it, cut out the fused section, rewind.
• Feeds too much line → worn bump knob/spring. Replace the head.
• Jams repeatedly → wrong diameter line. Switch to the specified size.

Related on GarageVetted

• Buying guide: Best String Trimmer to Pick in 2026
• How to Use a String Trimmer to Edge and Trim Like a Pro
• How to Choose a String Trimmer (Battery vs. Gas, by Yard Size)

Always match the line diameter to your string trimmer — going too thick can bog the motor or jam the spool. Wind in the direction of the arrow on the head, leave a few inches of leader, and feed it through the eyelet before you snap the cap back on your string trimmer. Check the owner’s manual for the exact line size your string trimmer needs.

For safe operating and line-handling tips before you restart your string trimmer, review the outdoor power equipment safety guidance at opei.org.