Open the head by locating the retaining cap or bolt
Most weed eater heads open one of two ways: by twisting off a cap, or by removing a bolt with a wrench or socket. Look at the top of the head — if you see a large plastic cap with ridges or knobs, grip it firmly and turn counterclockwise by hand. If the cap won't budge, wrap a cloth around it for grip. If you see a single bolt or hex nut instead, use the correct wrench size (usually 8mm, 10mm, or 13mm) and turn counterclockwise.
Once the cap or bolt is loose, set it aside in a safe place — these parts are small and straightforward to lose. The head will now separate into two halves: the top piece (the one you just opened) and the base that stays attached to the shaft. Some heads have a spring or washer underneath the cap; note which way it sits before you remove it completely, as it must go back the same way.
Key Takeaways
- Most weed eater heads open by twisting off a cap by hand, or by removing a single bolt with a wrench — check which type yours is before you start.
- The spool (the part that holds the string) usually stays in place; you remove only the top cap or bolt to access it.
- Wind new string onto the spool in the direction marked by an arrow on the spool itself, leaving 4 to 6 inches of string free on each side.
- Thread the free ends through the eyelets or holes in the head before reassembling, or the string will not feed out when you need it.
- Tighten the cap or bolt firmly by hand or wrench, but do not over-tighten — you can crack plastic heads this way.
Remove the spool and examine the string path
Once the cap is off, lift out the spool — it usually comes free by hand, though some models have a small pin or clip holding it in place. Look at the spool itself. You will see either two small eyelets (holes) on the sides of the head, or a slot or notch where the string feeds out. This is the string path, and you must thread your new string through it or the head will not work.
Check the spool for an arrow or directional marking. This arrow shows you which way to wind the new string. If there is no arrow, wind counterclockwise when looking down at the spool from above — this is the standard direction for most brands. Some spools have a small bump or guide that helps you wind neatly; use it if it is there.
Wind the new string onto the spool
Cut a length of string — usually 15 to 20 feet, depending on your head size. You can check the old string length if it is still intact, or look in your trimmer's manual. Insert one end of the string into the slot or notch on the spool where the old string was anchored. Some spools have a small hole; push the string end into it and pull tight so it does not slip.
Begin winding the string onto the spool in the direction the arrow points (or counterclockwise if there is no arrow). Wind it neatly in a spiral, keeping tension so the string does not bunch or overlap itself. Wind until you have about 4 to 6 inches of string left free — do not wind it all the way to the end. This free length is what you will thread through the eyelets and let hang out of the head so the trimmer can cut with it.
Thread the string through the eyelets or feed holes
Look at the edge of the head where the string comes out when you use the trimmer. You will see either two small holes (eyelets) on opposite sides, or a slot cut into the plastic. Take one of your free string ends and push it through one eyelet or into the slot. Pull it through until it hangs out the other side by 2 to 3 inches. Repeat with the other free end on the opposite side.
If your head has only one slot instead of two eyelets, both string ends go through the same slot — push one end in, then the other, so both hang out together. The string should be able to move freely through the holes; if it is stuck or kinked, pull it back out and straighten it before trying again.
Reassemble the head and test the fit
Place the spool back into the base of the head, making sure it sits flat and level. If there was a spring or washer under the cap, place it back on top of the spool in the same position it was before. Now lower the cap or top piece back onto the head, aligning any tabs or notches so it sits evenly.
If you removed a bolt, thread it back in by hand first to make sure it is going in straight — cross-threading will strip the hole. Once it is hand-tight, use your wrench to tighten it firmly, but stop before you feel strong resistance. Over-tightening can crack plastic heads or strip the bolt hole. If you removed a twist-on cap, turn it clockwise by hand until it is snug; you should not need a tool.
Trim the string to the correct length
Once the head is closed, the string hanging out of the eyelets is too long. Most trimmers cut string to the right length automatically the first time you use them, but you can trim it by hand if you prefer. The cutting line on most heads is 15 to 17 inches in diameter — measure from the center of the head outward to find where the string should end, or straightforward fire up the trimmer and let it cut the excess off.
If the string does not feed out when you use the trimmer, the most common cause is that you did not thread it through the eyelets before reassembling. Open the head again and check that both string ends are pushed all the way through and hanging free on the outside.
Troubleshoot if the head will not close or the string jams
If the cap or bolt will not tighten all the way, the spool may be sitting crooked. Open the head again, remove the spool, and look at the base — make sure there is no dirt, old string, or debris in the way. Clean it out with a dry cloth and try again. If the spool itself is cracked or warped, it will not sit flat and the head will not close properly; you may need to replace the entire spool assembly.
If the string jams or does not spin freely when you use the trimmer, the spool may be wound too tightly or the string may be twisted. Open the head, unwind a few loops, and rewind more loosely. Make sure the string is not kinked or bent where it enters the eyelets. A small amount of friction is normal, but the spool should spin by hand with light pressure.
Frequently Asked Questions
What size string do I need for my weed eater?
String diameter varies by trimmer model — common sizes are 0.065 inch, 0.080 inch, and 0.095 inch. Check your trimmer's manual or look at the packaging of the old string you removed. Using the wrong size can cause the head to jam or the string to break easily. Most hardware stores sell string in all three sizes, so you can bring the old string with you to match it.
Can I use any brand of string, or does it have to match my trimmer?
Any brand of string in the correct diameter will work. You do not need to buy the same brand your trimmer came with. Generic string from a hardware store costs less and performs the same way. The only exception is if your trimmer uses a specialty head (like a blade head or a bump-feed head) — in that case, follow your manual's recommendations for that specific head type.
How do I know if I wound the string the wrong direction?
If you wound it the wrong way, the string will not feed out smoothly or will jam when you use the trimmer. The arrow on the spool shows the correct direction. If you wound it backwards, straightforward open the head, unwind the string, and rewind it in the correct direction. It takes only a few minutes and is worth doing right the first time.
What if the cap is stuck and I cannot twist it off?
Soak the cap in warm water for a few minutes to loosen any dried grass or debris. Wrap a cloth around it for better grip and try again. If it is still stuck, use a rubber jar opener or a pair of pliers wrapped in cloth to avoid slipping and damaging the cap. Do not use excessive force — if it will not budge after soaking, the threads may be damaged and you may need a replacement head.
Do I need to replace the spool, or just the string?
In most cases, you only replace the string. The spool lasts for years if you wind it correctly and do not over-tighten the cap. Replace the spool only if it is cracked, warped, or the string slot is damaged. Many hardware stores sell replacement spools separately, which cost less than a full new head assembly.