How to Thread a Weed Eater Trimmer Head
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How to thread a weed eater comes down to a few steps: you cut two equal lengths of trimmer line, wind them onto the spool in the direction the arrow shows, feed the ends through the eyelets in the cutter head, and reassemble the head. The exact steps depend on your head design, so the first job is to find the spool and the line size your manual calls for. The walkthrough below uses a bump-feed head, the most common type on string trimmers, and cites a manufacturer procedure for the steps.
Quick answer
- Check your operator’s manual for the line type and diameter. The Troy-Bilt procedure cited below uses 10 feet of twin-strand line or two 10-foot lengths of .095 inch line.
- Disassemble the head: unscrew the bump knob, then remove the inner wheel and spring.
- Wind the line tightly onto the reel in the arrow direction, leaving about 6 inches free, and push the ends into the holding slots.
- Feed the ends through the eyelets, reseat the spring and wheel, and screw the bump knob back on.
Before you start: identify your head
Most trimmer heads fall into one of two groups. A bump-feed head releases more line each time you tap it on the ground. An auto-feed head releases line on its own when the trimmer runs. Threading instructions apply mainly to manual heads, so if your trimmer already uses automatic line feed, you may only need to replace a spool rather than thread a head.
Some heads are sold as universal parts. The listing for one universal trimmer head in our pack says it uses 2.0 mm or 2.4 mm round trimmer line, or smaller sizes, and that it has an M10 x 1.25 thread size with no hardware included. Another universal head in the pack lists a 110 mm by 75 mm size, a reverse screw nut of M10 x 1.25 mm, and adaptor bolts. Universal heads still need a check against your trimmer shaft and manual before you buy or install them.
Materials you need
- Trimmer line at the diameter and length in your manual. Do not use line thicker than the head rating.
- Scissors or a knife to cut the line cleanly.
- Your operator’s manual, which gives the spool direction and line length for your model.
- A clean, flat surface where small parts such as the spring and wheel will not roll away.
Step-by-step: thread a bump-feed head
The steps below follow the procedure Troy-Bilt publishes for bump-feed heads. Where your manual differs, follow the manual.
- Cut the line. Use 10 feet of twin-strand split line, or two 10-foot lengths of .095 inch line. Confirm the type in your manual.
- Disassemble the head. Unscrew the bump knob, then remove the inner wheel and the spring. Set the spring aside so it does not get lost.
- Start the line on the reel. Push one end of each line into one of the two holes on top of the inner reel. Pull them through until the ends are even, leaving 2 to 3 inches free.
- Close the loop. Push the short ends into the other hole, then pull the long end to close the loop.
- Wind the line. Follow the direction of the arrow on the top of the wheel and wind the trimmer line tightly around the spool.
- Secure the ends. When about 6 inches of line remain, push the ends into the holding slots.
- Feed the eyelets. Place the spring back on the shaft. Feed the line through the eyelets on the cutter head.
- Reassemble. Set the wheel back on the shaft, aligning its holding slots with the eyelets. Press the wheel down to compress the spring, then screw in the bump knob.
- Check the line. Gently pull both ends to confirm they are free of the holding slots and that each strand extends from the head.
The source uses a slot measurement that appears to be a typographic error. The line diameter it names, .095 inch, is the value to follow.
Common mistakes when threading
Most threading problems come from a small set of errors. The first is winding against the arrow. Line wound the wrong way can bind and fail to feed. The second is leaving the ends too short to seat in the holding slots, which lets the line pull free during use. The third is using a line diameter different from the one the head is rated for. A line that is too thick may not feed, and a line that is too thin may wear quickly. The fourth is forgetting the spring. Without it, the bump mechanism will not return and the head may not feed line at all.
If the line will not feed after you reassemble, take the head apart and check the eyelets. Line that is caught on the inside edge of an eyelet, or two strands that are not equal length, can stop feeding.
Heads in the pack that use manual or bump feeding
If you are replacing a head rather than re-threading an old one, these listings from our pack show the design features the listing states.
Universal trimmer head with a 49 ft line roll
This listing describes a universal trimmer head that fits most gas trimmers with curved or straight shafts, with M10 x 1.25 thread size. It includes 1 trimmer head and 1 roll of 49 ft by 0.09 inch trimmer line, and it lists 8 pivoting lines for cutting. The listing also states that the head is not compatible with a Stihl FS40 with fs80r, and that it is not recommended for bent shaft trimmers. The listing says no adapter is included.
Universal trimmer head with adaptor bolts
This head is described as a double-line bump-feed head with a 360 degree anti-wear line exit and a large-capacity line storage area. The listing says it comes with adaptor bolts that fit most brush cutters. It lists an approximate size of 110 mm by 75 mm and a reverse screw nut size of M10 x 1.25 mm. The listing does not state a line diameter, so check your manual before buying line for it.
Cordless weed wacker with auto line feed
This cordless model describes an automatic line feed system that senses the line length and extends line when more is needed. The listing says the built-in blade trims excess line at startup. It runs on two 2.5Ah batteries and the listing says runtime is about 40 minutes. Because the line feeds automatically, this design avoids the bump-and-thread routine described above. The listing does not give a line diameter.
How to decide between re-threading and replacing
Re-thread the head when the eyelets and holding slots are intact and the spool is the right size for your trimmer. Replace the head when the housing is cracked, the spring is missing or weak, or the bump mechanism no longer returns. A universal head can be a practical replacement, but only after you confirm its thread size and mounting against your shaft. The listing for each universal head should state the thread size and any fit limits, and the line should match the diameter in your manual.
FAQ
What line diameter should I use?
Use the diameter in your operator’s manual. The Troy-Bilt procedure cited in this article names .095 inch line for its bump-feed head. A universal head in our pack lists 2.0 mm or 2.4 mm round line, or smaller. Do not exceed the rating your manual gives.
How much line do I need?
The Troy-Bilt procedure uses 10 feet of twin-strand split line or two 10-foot lengths of .095 inch line. Your manual gives the length for your model, and the amount may differ.
Which way should the line wind?
Wind the line in the direction of the arrow on the top of the spool or wheel. Winding against the arrow can stop the line from feeding.
Why will the line not feed after I reassemble the head?
Check that the ends are seated in the holding slots, that both strands are the same length, and that the spring is back on the shaft. Look for line caught inside an eyelet.
Do all trimmers thread the same way?
No. Heads differ by brand and design. The Troy-Bilt steps are a bump-feed procedure, and the listing for one universal head says that assembly varies by attachment. Follow the manual for your model when it differs from this guide.
Bottom line
If your head is intact, cut the line your manual specifies, wind it in the arrow direction, seat the ends in the holding slots, and reassemble with the spring and wheel in order. If the head is damaged or will not feed after two attempts, replace the head instead of forcing the line.
Related reading: Top 10 Battery Powered Weed Eaters: 6 Real Picks Compared and Best Ryobi ONE+ String Trimmers Compared.
