The basic steps to replace trimmer line
Replacing the line on a string trimmer takes about five to ten minutes once you know the process. Most trimmers use one of two designs: a fixed spool that you wind by hand, or an automatic head that advances line as you tap it on the ground. The steps differ slightly, but both start the same way—stop the engine, let it cool for a few minutes, and flip the trimmer upside down so you can see the spool.
Before you begin, buy the correct line diameter for your trimmer. Check your owner's manual or look at the spool itself—the size is usually printed there. Common sizes are 0.065 inch, 0.080 inch, and 0.095 inch. Buying the wrong size means the line won't fit in the spool or won't feed properly. Most hardware stores and online retailers sell pre-wound spools that fit specific trimmer models, which is the easiest option if you don't want to wind line yourself.
Key Takeaways
- Stop the engine and let the trimmer cool completely before removing the spool, since the head gets hot during use.
- Check your owner's manual or the spool itself to find the correct line diameter—using the wrong size will cause feeding problems.
- For fixed spools, you wind new line by hand into the grooves; for automatic heads, you straightforward insert the line and let the mechanism feed it.
- Wind line tightly and evenly so it doesn't tangle, and leave a few inches of line sticking out on each side so the trimmer can cut.
- Test the trimmer at low speed first to make sure the line feeds smoothly before using it at full power.
How to remove the spool from your trimmer
The spool sits inside a plastic head at the bottom of the trimmer shaft. Most heads have a center bolt or a pair of tabs that you turn counterclockwise to loosen. Look for a bolt head or a slot that fits a wrench or screwdriver. Turn it slowly—some trimmers have reverse threads, so if it tightens instead of loosening, turn it the other way.
Once the bolt is loose, the entire spool assembly should come free in your hand. Set it on a clean surface so you don't lose any small springs or washers that might fall out. If your trimmer has an automatic head, there will be a spring underneath the spool—note which way it sits before you remove it, because it has to go back the same way or the line won't advance.
If the spool is stuck, spray a little penetrating oil around the bolt and wait a few minutes. Do not force it—forcing can crack the plastic head. Once it comes loose, wipe away any grass clippings or dirt from inside the head with a dry cloth.
Winding line on a fixed spool
A fixed spool has grooves or notches around the edge where you wind the line by hand. Cut a length of new line—usually between 20 and 30 feet, depending on the spool size. Your owner's manual will tell you the exact length, or you can measure the old line before you remove it.
Find the anchor point on the spool—a small notch or hole where one end of the line hooks in. Insert one end of the new line into this notch and hold it there with your thumb. Wind the line tightly and evenly around the spool, following the grooves. Keep tension on the line as you wind so it doesn't bunch up or overlap itself. Wind in the direction marked on the spool—usually counterclockwise when you're looking at the spool from above.
When you reach the end of the line, insert the other end into a second anchor notch on the opposite side of the spool. Leave about 4 to 6 inches of line sticking out on each side—this is what actually cuts the grass. If you leave too much, it will flap and wear out quickly; if you leave too little, the trimmer won't cut effectively.
Installing line in an automatic or tap-feed head
Automatic heads are simpler because you don't wind the line yourself. Cut two lengths of line, each about 15 to 20 feet long. Look for two small holes or slots on opposite sides of the spool—one for each line. Insert one end of the first line into one hole, pushing it all the way through until it comes out the other side.
Do the same with the second line in the other hole. Both lines should now pass through the spool with equal lengths sticking out on each side. Leave about 4 to 6 inches of line exposed on each side, just as you would with a fixed spool. The automatic mechanism will feed the line as you use the trimmer, so you don't need to worry about winding it tightly.
If your trimmer has a spring under the spool, make sure it's sitting in the same position it was before you removed the spool. The spring controls how the line advances, and if it's upside down or twisted, the trimmer won't feed line properly.
Reinstalling the spool and testing the trimmer
Slide the spool back into the trimmer head, making sure any springs or washers are in place. Screw the center bolt back in by turning it clockwise. Tighten it firmly but don't over-tighten—you should feel resistance, but you shouldn't have to strain. If you over-tighten, you can crack the plastic head or strip the threads.
Flip the trimmer right-side up and hold it away from your body. Start the engine and let it idle for a few seconds. Listen for the line feeding smoothly—you may hear a faint clicking or tapping sound as the automatic mechanism advances the line, or you may not hear anything at all. This is normal.
Increase the speed slowly to about half throttle and test the trimmer on a small patch of grass. The line should cut cleanly without stuttering or bunching. If the line isn't feeding or if it's wrapping around the spool, stop the engine when ready and check that the line is seated correctly in the spool and that the anchor notches are holding it in place.
Common mistakes that cause feeding problems
The most common mistake is winding the line too loosely or unevenly on a fixed spool. Loose line will tangle inside the head and jam the trimmer. Wind slowly and keep steady tension on the line the whole time. If you wind it too fast or without holding it tight, it will bunch up and cause problems.
Another mistake is leaving too much line sticking out. Line that extends more than 6 inches will flap and wear out in minutes, and the trimmer will vibrate more. Conversely, if you leave less than 3 inches, the trimmer won't cut effectively because there's not enough line to reach the grass.
Using the wrong line diameter is also common. If the line is too thin, it will break constantly. If it's too thick, it won't fit in the spool or feed properly. Always check your manual before buying new line.
When to replace the entire head instead of just the line
If the plastic spool is cracked, warped, or if the bolt threads are stripped, replacing just the line won't fix the problem. A damaged spool will cause the line to feed unevenly or not at all. Replacement heads are inexpensive—usually between $15 and $40—and they come pre-wound with line, so you can swap the entire assembly in a few minutes.
If the trimmer is several years old and the head is cracked, it's often cheaper to replace the head than to keep buying new line and dealing with feeding problems. Check the model number on your trimmer and search for a replacement head online or at a hardware store. Installation is the same as removing the old head—just unscrew the bolt and swap it out.
Frequently Asked Questions
How often do I need to replace the line?
This depends on how often you trim and what you're cutting. If you trim weekly in summer, you may need to replace the line every two to four weeks. If you hit rocks or hard objects, the line wears faster. Check the line before each use—if it's frayed, broken, or noticeably shorter than it was, it's time to replace it.
Can I use any brand of line in my trimmer?
As long as the line diameter matches what your trimmer needs, yes. Different brands vary slightly in thickness and material, but they all work the same way. Some people prefer thicker line because it lasts longer, while others prefer thinner line because it's quieter. Experiment to find what works best for your needs.
What if the line keeps breaking or won't feed?
First, check that you're using the correct diameter. If the diameter is right, the problem is usually that the line is wound too loosely or the spool is cracked. Remove the spool and inspect it for cracks or warping. If the spool looks fine, rewind the line more tightly and make sure both ends are seated firmly in the anchor notches.
Do I need to drain the fuel before replacing the line?
No, you don't need to drain the fuel. Just stop the engine and let it cool for a few minutes so the head isn't hot. Make sure the engine is completely off and won't accidentally start while you're working on it. If you're uncomfortable working on a running engine, you can remove the spark plug wire to prevent accidental starting.
How tight should I wind the line on the spool?
Wind it as tightly as you can while keeping it even and straight. The line should not be loose enough to move when you push on it with your finger. Think of it like winding a fishing reel—tight and even, with no gaps or overlaps. If you wind it too loosely, it will tangle inside the head.