The basic steps to swap out your trimmer line

Replacing trimmer line is a straightforward task that takes about five minutes once you know where to look. Most trimmers use one of two designs: a fixed spool that you wind by hand, or a bump-feed head that advances line automatically when you tap it on the ground. Both designs let you access the spool without tools, though the exact steps differ slightly.

The line itself comes in different thicknesses — typically .065 inch, .080 inch, and .095 inch — and your trimmer's manual or the spool housing will tell you which one fits yours. Buying the wrong thickness wastes money and can jam the head or break the line constantly. Most hardware stores and big-box retailers stock the common sizes in bulk spools, which costs less per foot than pre-wound cartridges.

Key Takeaways

  • Unplug the trimmer or remove the battery before opening the head, even though the motor is off — this prevents accidental startup.
  • Check your trimmer's manual or the spool housing for the correct line diameter, because using the wrong thickness causes jamming and breakage.
  • Fixed spools require you to wind the line by hand in the direction marked on the spool, while bump-feed heads use pre-wound cartridges you straightforward drop in.
  • Wind the line tightly and evenly, leaving about 6 inches of free line on each side of the spool to feed through the eyelets.

How to open the trimmer head

The head sits at the end of the trimmer shaft and is held on by a center bolt or a snap-ring. On most electric and battery trimmers, you'll see a single bolt in the middle of the spool — turn it counterclockwise by hand or with a wrench (usually 10mm or 12mm) until it comes free. On some models, the bolt has a left-hand thread, meaning it tightens counterclockwise and loosens clockwise, so check your manual if the bolt won't budge the first way you try.

Once the bolt is out, the spool housing lifts straight off. Set the bolt and any washers or springs in a small cup so you don't lose them — they all go back in the same order. If your trimmer has a snap-ring instead of a bolt, use a flathead screwdriver to pry it gently out of its groove, working your way around the ring so it doesn't bend.

Removing the old line from a fixed spool

A fixed spool has grooves or slots molded into it where the line sits. Pull out any remaining line — it may be wound tightly, so you may need to work it loose a bit at a time. Once the old line is out, wipe the spool clean with a dry cloth to remove grass clippings and dust, which can jam new line as it feeds.

Look for an arrow or the words "wind this way" molded into the spool. This direction matters because the line feeds out in the opposite direction as it rotates. If you wind it backward, the line will tangle or refuse to feed. The arrow usually points clockwise when you're looking at the spool from the front of the trimmer.

Winding new line onto a fixed spool

Cut a length of line — most spools hold between 15 and 25 feet, and your manual will specify the exact length. If you're not sure, cut about 20 feet and see how much fits; you can always cut more if you run out. Insert one end of the line into the small notch or hook at the edge of the spool (most spools have one to hold the line while you wind).

Wind the line tightly and evenly in the direction marked on the spool, keeping tension on the line with your other hand so it doesn't bunch up or cross over itself. Work your way across the spool from one side to the other, filling the grooves completely. When you reach the other side, leave about 6 inches of free line hanging out, then insert that end into the second notch or hook on the opposite side of the spool.

The two free ends of line are what feed through the eyelets (the small holes in the trimmer head) when you reassemble everything. If you wind the line all the way to the end with no free line left, it won't feed out when you start trimming.

Installing a bump-feed cartridge

Bump-feed heads use a pre-wound cartridge that you straightforward drop into the housing — no winding required. The cartridge is a plastic spool with line already wrapped around it, and it costs a bit more than bulk line but saves time. Remove the old cartridge by pulling it straight out of the housing.

Insert the new cartridge into the housing, making sure the two free ends of line (usually about 4 to 6 inches each) are pointing outward through the eyelets. The cartridge should sit flat and flush against the bottom of the housing. If it doesn't sit evenly, remove it and check that you haven't twisted it as you inserted it.

Reassembling the trimmer head

Before you bolt the head back on, thread the two free ends of line through the eyelets on the trimmer head. The eyelets are small holes, usually two of them, positioned around the edge of the head where the line exits. Pull each end through gently — the line should feed smoothly without resistance.

Once both ends are threaded, place the spool back into the housing and align the center bolt hole. Insert the bolt and any washers or springs in the same order they came out, then turn the bolt clockwise by hand until it's snug. Don't over-tighten — you only need enough pressure to hold the spool in place. If you're using a wrench, tighten until you feel resistance, then give it a quarter turn more.

Trim the free ends of line to about 2 to 3 inches each — this is the working length that cuts the grass. Plug the trimmer back in or reinsert the battery, then test it briefly in an open area away from people and pets to make sure the line feeds and spins freely.

Troubleshooting common problems

If the line won't feed out when you start trimming, the most common cause is that you didn't leave enough free line on the spool before reassembling. Open the head again and check that at least 6 inches of line is hanging loose on each side. If the line is wound too tightly or bunched up, the spool can't rotate freely enough to feed new line out.

If the line keeps breaking or shredding, you may be using the wrong diameter for your trimmer. Check your manual and compare the line you're using to the specification. Thick line on a trimmer designed for thin line will jam and snap; thin line on a trimmer designed for thick line will break under the stress of cutting. Another cause is debris or dried grass stuck in the eyelets — clean them out with a small brush or cloth before you start trimming again.

If the line tangles or twists as you wind it, you're likely winding too loosely or not keeping tension on it. Unwind what you've done, start over, and keep steady pressure on the line with your other hand the entire time you're winding. The line should feel snug and even across the spool with no gaps or overlaps.

Frequently Asked Questions

Can I use any thickness of trimmer line in my trimmer?

No. Using the wrong thickness causes jamming, breakage, and poor cutting. Check your trimmer's manual or the spool housing for the correct diameter — usually .065, .080, or .095 inch. Using thicker line than your trimmer is designed for will strain the motor and jam the head.

How often do I need to replace the trimmer line?

It depends on how often you trim and the thickness of the vegetation. Most homeowners replace the line every few months during the growing season. You'll know it's time when the line breaks frequently, wears down to less than an inch on each side, or stops cutting cleanly.

What's the difference between fixed spool and bump-feed heads?

Fixed spools require you to wind the line by hand and are cheaper to maintain. Bump-feed heads use pre-wound cartridges that advance automatically when you tap the head on the ground — they cost more per replacement but save time and effort.

Do I need tools to replace the trimmer line?

You may need a wrench (usually 10mm or 12mm) to remove the center bolt, but most bolts can be turned by hand. A flathead screwdriver helps if your trimmer uses a snap-ring instead of a bolt. Beyond that, no special tools are required.

Why does my line keep tangling when I wind it?

Tangling usually means you're not keeping steady tension on the line as you wind, or you're winding too loosely. Hold the line firmly with your other hand and wind it tightly and evenly across the spool. If it still tangles, unwind and start over — rushing the process causes most winding problems.