How to Replace String in Your Weed Eater

The basic steps to load new string

Replacing the string in a weed eater is a straightforward task that takes about five minutes once you know the steps. Most weed eaters use one of two designs: a fixed spool that you wind by hand, or an automatic or semi-automatic head that advances string as you tap the head on the ground. The method differs slightly between them, but both start the same way: stop the engine, let it cool, and remove the spool or head from the shaft.

Before you begin, buy the correct string diameter for your model. Check your owner's manual or the side of 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. Have your replacement string on hand before you take the head apart.

Key Takeaways

Stop the engine and let it cool completely before removing the spool or head.
Check your manual or the head itself to find the correct string diameter for your model.
On a fixed spool, wind the string tightly in the direction marked on the spool, leaving 6 to 8 inches free on each side.
On an automatic head, thread the string through the eyelets and wind it around the spool in the marked direction.
Reassemble the head, thread the free ends through the eyelets, and trim them to the length marked on the head.

Removing the spool or head from the shaft

The head screws onto the drive shaft at the end of the boom. Most heads turn counterclockwise to unscrew, but some turn clockwise—your manual will tell you which. Grip the shaft with one hand to keep it from spinning, then turn the head counterclockwise (or clockwise, depending on your model) with the other hand until it comes free.

Once the head is off, you will see either a fixed spool inside or a cartridge-style head. If you have a fixed spool, you may need to remove a cover or cap to access it. Some models have a small bolt or clip holding the spool in place—remove that first. Set all small parts in a clean spot where you will not lose them.

Replacing string on a fixed spool

A fixed spool is a round plastic drum with grooves or a channel around the edge. Look for an arrow or marking on the spool showing the direction to wind. Cut a piece of string about 20 feet long (you can trim it later). Insert one end into the small notch or hole at the edge of the spool, then wind the string tightly around the spool in the marked direction, keeping tension as you go.

Wind until you have about 6 to 8 inches of string left unwound. Insert the free end into the second notch or hole on the opposite side of the spool. Wind the remaining string in the same direction until both sides are wound evenly and the spool is full. The string should sit snugly in the grooves without overlapping itself.

Reassemble the spool cover or cap, then screw the head back onto the shaft. Thread the two free ends through the eyelets (the small holes at the edge of the head where the string exits). Trim each end to the length marked on the head—usually 8 to 10 inches. Start the engine and test it; the string should spin freely without wobbling.

Replacing string on an automatic or semi-automatic head

Automatic heads advance string automatically when the engine idles; semi-automatic heads advance it when you tap the head on the ground. These heads usually have a cartridge or spool inside that you can access by removing a cover. Some models let you replace the entire cartridge as a unit; others let you wind new string onto the existing spool.

If you are winding string onto the existing spool, look for the starting notch or hole marked on the spool. Insert one end of your string (cut to about 20 feet) into that notch and wind tightly in the direction marked on the spool. Wind until you have 6 to 8 inches left, then insert the free end into the second notch and wind the remaining string the same way. Keep tension even so the string sits flat and does not overlap.

If your model uses a cartridge, straightforward remove the old one and snap the new one in place. Cartridges come pre-wound, so you only need to thread the free ends through the eyelets and trim them to the marked length. Reassemble the head cover, screw the head back onto the shaft, and thread the string ends through the eyelets on the head itself.

Threading and trimming the string

Once the head is back on the shaft, you will see two small eyelets or holes where the string exits the head. Thread one free end through each eyelet so the string hangs out evenly on both sides. The string should move freely through the eyelets without binding.

Trim each end to the length marked on the head or in your manual. Most heads are marked with a line or notch showing the correct length—usually 8 to 10 inches per side. Use scissors or a utility knife to cut a clean, straight edge. Uneven or too-long string will cause vibration and uneven cutting.

Testing and troubleshooting

Start the engine and let it run at idle for a few seconds. The string should spin smoothly without wobbling or hitting the guard. If it wobbles, the string may not be wound evenly on the spool—stop the engine, let it cool, and rewind it more carefully, keeping even tension throughout.

If the string does not advance on an automatic head, the spool may not be seated correctly. Stop the engine, remove the head, and check that the spool is fully inserted and the cover is snapped on tight. If the string jams or breaks quickly, you may have the wrong diameter—check your manual and buy the correct size.

When to call a professional

If the head itself is cracked, the eyelets are broken, or the spool will not turn freely even after you have removed all string, the head may need to be replaced. A new head costs between $15 and $40 depending on the model.

If you are not comfortable removing and reassembling the head, or if the engine will not start after you have reinstalled it, take the weed eater to a small-engine repair shop. A technician can diagnose whether the problem is the head, the fuel line, the spark plug, or something else on the engine itself.

Frequently Asked Questions

How often should I replace the string?

String wears down with use and breaks when it hits rocks or thick weeds. Most people replace it every few months during the mowing season, or whenever it breaks. Keep a spool of replacement string on hand so you are not caught without it mid-season.

Can I use any brand of string?

Any string of the correct diameter will work in your head. Brands vary slightly in durability and how long they last, but they all function the same way. Buy the diameter your manual specifies; the brand matters less than the size.

What if I wind the string in the wrong direction?

If you wind it backward, the string will unwind as the spool spins and you will run out of string quickly. Stop the engine, let it cool, remove the head, and rewind it in the correct direction marked on the spool. It is an straightforward fix.

How tight should I wind the string?

Wind it snugly so it does not slip on the spool, but not so tight that you strain your hands or the spool warps. The string should sit flat in the grooves without overlapping itself. If you are winding by hand, moderate tension is usually right.

Why does my string keep breaking?

The most common causes are using the wrong diameter, winding it unevenly so it jams, or hitting rocks and hard objects. Check that you have the correct size for your model. If the diameter is right, rewind the spool more carefully, keeping even tension throughout.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.