Replace the head by removing the old spool, installing a new one, and threading fresh line through it

A weed eater head (also called a trimmer head or cutting head) holds the nylon line that does the cutting. When the line breaks or wears down, you can buy a replacement head as a complete unit and swap it out in about 10 minutes. Most homeowners can do this without tools or special knowledge — you just need to know which direction to turn and how your particular head releases the old spool.

The exact steps depend on whether your head uses a fixed spool, a bump-feed spool, or an automatic spool. All three types work the same basic way: unscrew the old head, screw on the new one, and load it with line. The differences are in how you thread the line and whether you need to wind it yourself or buy it pre-wound.

Key Takeaways

  • Most weed eater heads unscrew counterclockwise from the shaft, but some screw clockwise — check your manual or look for an arrow on the head itself.
  • Replacement heads come pre-wound with line already loaded, or empty so you can wind your own — buy whichever type matches your trimmer model.
  • After installing the new head, you may need to tap it on the ground to feed out fresh line, depending on whether your head is automatic or manual.
  • If the head spins but the line does not feed out, the spool may be stuck or the line may be wound too tightly — tap harder or loosen the spool slightly.

Identify your weed eater head type before you buy a replacement

The three common types are fixed spool (line does not move unless you manually pull it), bump-feed (tap the head on the ground to release more line), and automatic (line feeds out on its own as it wears). Look at your trimmer head right now: if there is a button or knob on top, it is likely automatic or bump-feed. If the head is smooth on top, it is probably fixed spool.

Check your trimmer's manual or the manufacturer's website to confirm the head type and find the exact model number. Write down that number before you go to the store or order online — buying the wrong head type means wasted money and a trip back. Home Depot, Lowe's, and Ace Hardware all stock common replacement heads, and they can look up the right one if you give them your trimmer brand and model.

Remove the old head by turning it counterclockwise

Stop the engine and let it cool for at least five minutes. Locate the shaft — the metal rod sticking up from the trimmer body. The head screws onto the top of this shaft. Most heads unscrew counterclockwise (turn left), but some screw clockwise (turn right). Look for an arrow or text on the head itself that says which way to turn, or check your manual.

Grip the shaft firmly with one hand to keep it from spinning, then turn the head with your other hand. If it is stuck, spray a little penetrating oil (like WD-40) around the base where the head meets the shaft, wait two minutes, and try again. Once it starts turning, keep going until the head comes free. Set it aside — you will not need it again unless you want to keep it as a backup.

Install the new head by screwing it on clockwise or counterclockwise

Take the new head out of the box and check that it came with line already loaded, or that you have the right type of line to wind yourself. Screw the new head onto the shaft using the same direction you unscrewed the old one — if the old one came off counterclockwise, the new one goes on counterclockwise. Hand-tighten it until it is snug; do not use a wrench or pliers, because you can crack the plastic head.

If your new head came pre-wound with line, you are done with installation. If it came empty and you need to wind line yourself, you will do that in the next step. Most people buy pre-wound heads because they are faster and less fiddly, but empty heads are cheaper if you already have line at home.

Load line into an empty head if yours did not come pre-wound

If your new head is empty, you will need to wind nylon line onto the spool inside. The line thickness matters — common sizes are 0.065 inch, 0.080 inch, and 0.095 inch. Check your manual to find the right size for your trimmer, or look at the old line if you still have it. Buy a spool of line at any hardware store or online.

Open the head by unclipping or unscrewing the cover (check your manual for the exact method). Pull out the empty spool. Look for two small slots or holes on opposite sides of the spool — these are where the line anchors. Cut a piece of line about 15 to 20 feet long, insert one end into a slot, and wind the line tightly around the spool in the direction shown by an arrow on the spool itself. When you reach the other slot, insert the end there to anchor it. Close the cover and reinstall the head on the shaft.

Feed out line and test the head before you trim

If your head is automatic or bump-feed, tap the bottom of the head firmly on the ground a few times. This releases fresh line from the spool. You should see new line appear at the cutting edge. If nothing happens, tap harder or check that the spool is not wound so tightly that it is stuck.

If your head is fixed spool, you may need to manually pull the line out to the cutting edge. Some fixed-spool heads have a small lever or button you press to release line; others you just pull by hand. Check your manual to see which applies to yours.

Start the engine and let it idle for a few seconds. The spinning line should trim grass cleanly. If the line is not spinning or is barely moving, stop the engine, let it cool, and check that the head is screwed on tightly. If it is tight and the line still will not spin, the problem is likely with the engine or drive shaft, not the head — that is when you call a repair shop.

Frequently Asked Questions

Can I reuse my old head instead of buying a new one?

Yes, if the spool is not cracked and the line is not completely worn away. You can wind new line onto the old spool and reinstall it. This saves money if you already have line at home, but most people find it easier to buy a pre-wound replacement head for $15 to $30 than to spend 20 minutes winding line by hand.

What if the head spins but the line does not come out?

The spool is probably wound too tightly or the line is stuck. Stop the engine, let it cool, and tap the head on the ground harder — use the force you would use to tap a nail into wood. If that does not work, unscrew the head, open it, and loosen the spool slightly by hand. Do not force it or you may crack the plastic.

How do I know what size line to buy?

Check your trimmer's manual for the line diameter — common sizes are 0.065, 0.080, and 0.095 inch. If you do not have the manual, look at the old line if you still have it, or take a photo of your trimmer to a hardware store and ask. Using the wrong size can make the trimmer work poorly or damage the head.

Do I need to replace the head if the line just broke?

No. If the head itself is not cracked and the spool spins freely, you can wind new line onto the old spool and keep using it. You only need a new head if the plastic is cracked, the spool does not spin, or the line will not feed out no matter how hard you tap it.

Can I use any brand of replacement head on my trimmer?

No. Heads are made for specific trimmer models and brands. Using the wrong head can cause it to fall off or not spin. Always buy a head made for your exact trimmer model — the box will say which brands and models it fits. When in doubt, ask at the store or call the trimmer manufacturer.