The Basic Steps to Load New String

Replacing the string on a weed wacker takes about five to ten minutes once you know the process. Most weed wackers use one of two designs: a fixed spool that you wind by hand, or an automatic head that advances string as you tap it on the ground. The steps differ slightly between them, but both start the same way — you remove the spool, empty the old string, and measure out new line.

Before you start, buy the correct string diameter for your machine. Check your weed wacker's manual or the label on the head itself — common sizes are 0.065 inch, 0.080 inch, and 0.095 inch. Using the wrong diameter can jam the head or break the string constantly. Most hardware stores sell spools of replacement string in all three sizes, usually labeled by brand name and diameter.

Key Takeaways

  • Turn off the engine and let the weed wacker cool for at least five minutes before touching the string head.
  • Check your manual or the label on the head to find the correct string diameter — using the wrong size will cause jams or breakage.
  • On a fixed spool, wind the string tightly in the direction marked by the arrow, keeping tension even as you go.
  • On an automatic head, insert the string into the slot, wind it around the spool, and tap the head on the ground to advance it as it wears.
  • Leave a small amount of string sticking out of the head — usually two to three inches — so the trimmer can cut it to the right length on first use.

Preparing the Weed Wacker and Removing the Old String

Start by turning off the engine and unplugging the spark plug wire if your weed wacker is gas-powered. Let the head cool for at least five minutes — the string can be hot enough to burn your skin. For electric models, unplug the cord from the outlet.

Locate the center bolt or cap on the string head. Most weed wackers have a single bolt in the middle that holds the spool in place. Turn it counterclockwise by hand or with a wrench — the size varies by brand, but usually falls between 8 and 10 millimeters. Once the bolt is loose, the entire spool should lift out. Pull out any remaining old string and discard it.

Winding String on a Fixed Spool

A fixed spool is the most common design. Look for an arrow printed or molded into the spool showing the direction to wind. This direction matters — winding backward will cause the string to tangle or slip when you start the engine.

Cut a length of new string, usually between 20 and 25 feet depending on your spool size. Your manual will specify the exact length. Insert one end of the string into the small notch or hole at the edge of the spool — most spools have a slot designed to hold the starting end. Wind the string tightly around the spool in the direction the arrow points, keeping even tension as you go. Do not let the string bunch up or overlap itself, or it will jam when you try to use it.

Wind until you reach the end of the string. Tuck the final end into the slot on the opposite side of the spool, or into a notch designed to hold it. Leave about two to three inches of string hanging out past the edge of the spool — the trimmer head will cut this to the correct length the first time you use it. If you leave too much, it will drag on the ground; too little, and the head may not cut properly.

Loading String on an Automatic Head

An automatic head advances string as you use it, so you do not have to wind it by hand. Instead, you insert the string into a slot on the spool and wind it a few times to hold it in place.

Cut a length of string — usually 15 to 20 feet for an automatic head, though check your manual. Find the slot or hole on the edge of the spool and insert one end of the string. Wind the string around the spool two or three times in the direction marked by the arrow, keeping it tight. Tuck the end into the slot to hold it. Leave two to three inches of string sticking out, just as you would with a fixed spool.

Automatic heads work by tapping the bottom of the head on the ground while the engine is running. This impact triggers a mechanism that releases a small amount of new string from the spool. If you wind too much string or wind it loosely, the head will jam or advance too much string at once.

Reinstalling the Spool and Testing

Once the string is wound and seated in the slots, lower the spool back into the head. Line up the center hole with the bolt hole, then turn the center bolt clockwise by hand until it is snug. Do not over-tighten — you only need enough pressure to hold the spool in place. If you strip the bolt, you will have to replace the entire head.

Before you start the engine, spin the spool by hand to make sure the string does not catch or bind. It should rotate smoothly in both directions. If it catches, the string is wound too loosely or is tangled — remove the spool and rewind it.

Start the engine and let it run at idle for a few seconds. The string should not move on its own. If it does, the spool is not seated correctly or the bolt is loose. Stop the engine, let it cool, and check the bolt again.

Common Mistakes That Cause Problems

The most frequent error is winding the string in the wrong direction. If the string does not advance or tangles when ready when you start the engine, you wound it backward. Remove the spool and rewind it in the opposite direction.

Another common problem is leaving too much string hanging out. When you first use the weed wacker, the string will drag on the ground and may wrap around the shaft. Trim it back to about half an inch with scissors or a utility knife before the next use.

Using the wrong string diameter will cause the head to jam or the string to break constantly. If you are not sure which size your machine takes, check the label on the head itself or look up your model number online. Buying the correct size once saves frustration later.

Winding the string too loosely is another cause of jams. The string should be tight enough that you feel resistance as you wind, but not so tight that you strain your hand. If the string slips when you tug it, unwind and start over with more tension.

When to Replace the Entire Head

If the spool cracks, the bolt threads strip, or the head no longer advances string smoothly, you may need to replace the entire head rather than just the string. Replacement heads cost between $15 and $40 depending on your weed wacker brand and model. They install the same way the old one came off — unbolt the damaged head and bolt on the new one.

Some weed wackers use proprietary heads that only fit that brand. Before you buy a replacement, check whether your model uses a standard universal head or a brand-specific one. Universal heads fit most weed wackers and cost less, but brand-specific heads may last longer because they are designed for your exact machine.

Frequently Asked Questions

How often do I need to replace the string?

String wears down with use and breaks when it hits rocks or thick weeds. Most people replace it every few weeks during heavy use, or once or twice a season for light use. You will know it is time when the trimmer stops cutting cleanly or the string breaks repeatedly.

Can I use any brand of string, or does it have to match my weed wacker?

Any brand of string works as long as the diameter matches what your head requires. The brand name does not matter — what matters is the thickness. Buy the correct diameter and you are fine.

What if the string keeps breaking right after I load it?

Check that you are using the correct diameter for your machine. If the diameter is right, the string may be wound too loosely or the spool may be damaged. Try rewinding with more tension. If it still breaks, the spool may have a crack or burr that is cutting the string — you may need a replacement head.

Do I have to let the engine cool before replacing the string?

Yes. The string head gets hot during use and can burn your skin. Always turn off the engine, unplug the spark plug wire or power cord, and wait at least five minutes before touching the head.

Why does my automatic head not advance string when I tap it on the ground?

The string may be wound too tightly, or the mechanism inside may be jammed with grass or dirt. Try removing the spool and rewinding with slightly less tension. If that does not work, clean out any debris from the head with a brush and try again.