How to Restring a Weed Eater

1. First, Identify Your Trimmer Head

Every weed eater uses one of a handful of head designs, and the restringing method depends entirely on which one is on yours. Before you cut any line, look at the head. Does it have a bump knob on the bottom and a cap held on by tabs? Does it have arrows on the side and a hole running straight through? Is there a button? Does a single line come out of one side only? Those clues tell you which section of this guide to follow.

Your owner manual is the final word on two numbers: the line diameter the head accepts and the length to load. If you have lost the manual, most manufacturers post them on their websites by model number, which is printed on a sticker on the shaft or motor housing. The head itself often carries the maximum diameter molded into the plastic. Those numbers matter more than anything on the line packaging, because a head that is overfilled or loaded with line that is too thick will weld and jam.

Before you touch the head, make the tool safe. On a battery trimmer, remove the battery. On a corded model, unplug it. On a gas trimmer, switch it off and pull the spark plug boot so it cannot fire if you spin the head by hand. It sounds like overkill, but you are going to have your fingers in the cutting head, turning it, and a trimmer that starts unexpectedly will spin the line at full speed. It takes ten seconds and it is the only real injury risk in this job.

Finally, clear the head. Grass wraps around the shaft and packs into the spool housing, and caked debris is one of the most common reasons a freshly wound head will not feed. Pull out the old line and any grass, wipe the inside of the housing, and check the eyelets where the line exits. If they are grooved or chipped from years of use, replace them or the head, because a sharp-edged eyelet will cut through new line over and over.

2. Restringing a Standard Bump-Feed Head

The classic bump-feed head is the one most people mean when they say restring. Press the release tabs on the side of the cap or unscrew the bump knob, depending on the design, and lift off the cover. Take out the spool and note how it sits, including any spring underneath, because the spring is what pushes the spool back into its locked position after each bump. Lose the spring and the head will either feed nonstop or not at all.

Cut the length your manual specifies. For dual-line heads that is usually somewhere between about 10 and 20 feet in total; Ryobi, for example, calls for 16 feet in its Reel Easy head, and Husqvarna rates its T25 head to hold about 16.5 feet of .095 inch line. Too much line overfills the spool and causes welding and jamming. Too little means you will be doing this again in fifteen minutes. If you are unsure, start with less; it is far easier to add than to unwind a jammed spool.

Most modern dual-line spools are split into two channels with a slot or hole in the divider. Fold the line in half, hook the midpoint into that center slot, and you have two equal ends, one for each channel. Older designs have two separate holes, one per channel, and you thread each end in separately. Either way, the line has to be anchored at the spool so it does not just spin loose when the head rotates.

Now wind. Look for the arrow molded into the spool and wind in that direction, keeping each line in its own channel. Wind tight, under tension, in neat side-by-side rows, like thread on a sewing machine bobbin. Loose wraps shift under centrifugal force, cross over each other and melt together. Stop when the line is a little below the rim of the spool, leaving the last several inches unwound. Clip each end into the small notches on the spool edge to hold it while you reassemble.

Thread each end through its eyelet in the housing, seat the spool and spring, and push the cap on until the tabs click, or screw the bump knob back on. Pull both lines firmly to free them from the holding notches and let them feed out. Trim them so they are equal and do not extend past the cutoff blade on the guard. Unequal lengths make the head vibrate. Give the bump knob a few taps with the tool off to confirm the line advances, then reinstall the battery or plug.

3. Speed-Load Heads: No Disassembly

Speed-load heads exist because almost everyone hates taking a bump head apart. Instead of removing the spool, you feed a length of line straight through a channel in the head until equal lengths stick out of both sides, then turn a knob or the spool itself to wind it in. No cap, no spring, no fumbling with notches. If your trimmer has arrows or alignment marks on the outside of the head and a hole that goes clean through, it is probably one of these.

Ryobi Reel Easy heads follow the pattern exactly. Ryobi instructs you to turn the bump knob until the white markers on the side line up, feed about 16 feet of line through the eyelet until equal amounts hang out each side, then twist the knob clockwise until about six inches remain on each side. The head is compatible with .080, .095 and .105 inch line, and Ryobi sells an optional crank-style Speed Winder that does the twisting for you.

Echo Speed-Feed 400 heads work the same way in three steps: line up the arrows, feed the line, and twist the top knob. Stihl AutoCut C 26-2, which is fitted to many of its gas trimmers, has you push the line through the eyelet until it emerges on the other side, center it, then turn the spool in the direction of the arrows until the ends sit near the line limiter, trimming any excess. Stihl rates it to hold up to about 8 meters of 2.4 mm line, which is .095 inch, or about 7 meters of 2.7 mm.

EGO Powerload, fitted to trimmers such as the ST1521S in our best weed eater guide, takes the idea further. You thread the line through the head, pull it so both sides are even, and press the load button; the motor winds the line onto the spool for you. EGO ships it with .095 inch twisted line. The only catch with any speed-load head is that the line must be cut cleanly, ideally at a slight angle, so it slides through the channel without snagging inside.

Two cautions apply to every speed-load head. The first is alignment: if the markers or arrows are not lined up, the line hits the spool wall and will not pass through, and forcing it bends the end. The second is fill. It is tempting to load the whole length the head will hold, but a spool packed to the rim is the classic cause of welding. Load the length the manual recommends and no more.

4. Auto-Feed Spools and Fixed-Line Heads

Many lightweight battery trimmers do not use a bump head at all. Black and Decker AFS models and Worx trimmers with Command Feed, including the WG163 in our weed eater tests, run a single strand of .065 inch line from a small spool and advance it automatically or at the press of a button. On these, restringing usually means swapping the spool: pop off the cap, pull out the empty spool, drop in a pre-wound one, thread the line end through the eyelet, and snap the cap back on.

You can rewind these spools yourself with bulk .065 line, and it saves money, but they are less forgiving than dual-line heads. The line has to be wound very tightly and evenly in the direction of the arrow, with no crossed wraps, and the end has to sit in the retaining slot so it does not unravel while you reassemble. Loosely hand-wound line is the most common reason auto-feed trimmers jam or feed too much. If yours keeps misbehaving after a rewind, a factory spool is usually worth the extra few dollars.

Fixed-line heads are at the other end of the scale. Instead of a spool, they take pre-cut lengths of line pushed through holes in the head and locked in place. Nothing feeds out automatically; when a line wears down, you pull it out and push a new piece in. They are popular on professional gas trimmers and brushcutters because there is nothing to weld or jam, and they handle heavy line in tough growth. The trade-off is that you stop more often to replace short lengths.

To reload a fixed-line head, cut lengths to the size the head specifies, or buy pre-cut line in that length and diameter. Insert each piece through its hole until the stop or locking point engages, and make sure both sides end up the same length so the head stays balanced. Because the line does not wrap around anything, square and multi-sided profiles that tend to bind in spools work fine here.

5. Line Diameter and Shape by Trimmer Class

Line diameter is the setting most people get wrong, usually by going thicker in the hope of breaking less line. Thicker line does cut heavier weeds and lasts longer against fences, but it is heavier and has more drag, so it loads the motor, cuts head speed and shortens battery runtime. Put line that is too thick in a small trimmer and it bogs, overheats and welds in the spool. Use the size your trimmer is rated for, and treat the maximum on the head as a hard limit.

Shape matters too. Round line is the durable all-rounder: it wears slowly, resists breaking when it slaps a fence or a driveway edge, and is the right choice if most of your trimming is along hard surfaces. Twisted line, which EGO ships with Powerload, has a spiral profile that cuts with less noise and drag than round line of the same diameter. Square and other multi-sided profiles have sharp edges that slice thick weeds cleanly, but those edges wear down quickly against concrete and stone.

Dual line versus single line comes down to the trimmer. Two lines make two cuts per revolution, so a dual-line head clears grass faster and leaves a cleaner finish, at the cost of more drag and more power draw. That is why small battery trimmers often use a single line: it stretches runtime. On a high-voltage battery or gas trimmer with power to spare, dual line is the better cutter. Our best string trimmer comparison covers line systems model by model.

Quality varies more than the packaging suggests. Cheap line is often more brittle and more prone to welding and snapping, and premium co-polymer lines generally last longer per foot. You do not need the most expensive line on the rack, but a mid-priced name brand line in the correct diameter usually costs less over a season than a bargain spool that breaks every few minutes.

6. Soaking Trimmer Line: Myth or Fact?

You will hear that soaking trimmer line in water makes it last longer, and it sounds like a garage myth. It is mostly fact. Trimmer line is made of nylon, and nylon is hygroscopic: it absorbs moisture from the air, and absorbed water acts as a plasticizer, making it more flexible and less brittle. Line that has sat on a shelf in a hot, dry garage for a year or two loses moisture and becomes stiff, and stiff line snaps and welds far more easily.

There is real data behind this. Patent filings from trimmer line manufacturers describe 24-hour soaking tests in which line gained roughly 3.6 to 6.4 percent of its weight in moisture, with thinner line absorbing proportionally more. The official Stihl New Zealand store advises soaking new line in water for at least 24 hours before loading to restore its elasticity, and the advice to keep spare line moist shows up in manufacturer guidance and pro forums alike.

Keep it in proportion, though. Soaking helps line that has dried out; it does little for fresh line from a sealed package, and it will not fix line that is the wrong diameter, a spool wound loosely, or a worn eyelet. Line that is stored sealed and kept out of the heat holds its moisture far better, which is why fresh stock rarely needs the treatment. Soaking is a cheap improvement for old stock, not a cure for a head that is set up wrong.

If you want to do it, cut the length you need, coil it loosely, and leave it in a bucket of water overnight before winding. Store spare line in a sealed bag or container out of direct sun, away from heat sources like the water heater, so it does not dry out to begin with. Dry wet line off before winding so you are not loading water into a battery tool head.

7. Troubleshooting: Welding, Not Feeding, Snapping

Line welding, where the wraps on the spool melt together into a solid lump, is caused by heat and pressure. The head spins very fast, line rubs against line, and in hot weather that friction is enough to fuse nylon. The common triggers are an overfilled spool, loose wraps that shift and cross, line thicker than the head was designed for, and dry, brittle line. Rewinding tightly, stopping short of the rim, keeping the two lines in separate channels, and using the correct diameter fix most cases.

If line will not feed when you bump, start with direction: a spool wound against the arrow cannot pay out. Next, check that the ends are long enough to catch, since bump heads need several inches of line outside the eyelets to have something to fling outward. Then look for a missing or weak spring, a bump knob worn smooth, or line welded on the spool. Bump the head on soil or grass at full speed, not at idle, because the head relies on centrifugal force to draw the line out.

Auto-feed single-line trimmers have their own failure: feeding too much, or not feeding at all. Usually the line was wound loosely, the end slipped out of its retaining slot, or the spool was not seated fully against its spring. Rewind it tightly or fit a factory spool. If the line keeps snapping off at the eyelet, the eyelet is probably worn and sharp-edged and needs replacing. If it breaks mid-length, the line is likely old, dry or too thin for the work.

Snapping is often a technique problem. The line cuts at its tip, where speed is highest, so plunging the whole head into dense weeds or holding it against a fence or a concrete edge chews through line in seconds. Work with the tip, take thick growth down in layers, and approach hard edges at a slight angle. When you are edging along a driveway, keeping the crack line clear also helps; our guide to killing weeds in driveway cracks covers the long-term fix so you are not grinding line on concrete every week.

Finally, maintain the rest of the tool, because a weak trimmer feeds poorly. A clogged air filter or old fuel on a gas trimmer and a tired battery on a cordless one both reduce head speed, and lower speed means less force to pull line out. Pair a well-set-up trimmer with a good leaf blower for cleanup and sharp mower blades, and a weekly yard routine stays quick.