How Do You Put Line in a Weed Eater? (Step-by-Step Guide for All Head Types)

What Type of Weed Eater Head Do You Have?

Head type determines the entire reloading process. Identify yours before purchasing line or starting any steps.

• Bump-feed head: The most common consumer head type. Features a round plastic bump knob on the bottom. You tap the knob against the ground while the trimmer runs to advance line. The spool winds two lengths of line internally. If your trimmer has a protruding center knob you can press, this is your head type.
• Auto-feed head: Advances line automatically using centrifugal force as the head spins — no tapping required. Often found on mid-range electric and battery trimmers. Recognized by the absence of a bump knob and a spring-tensioned internal mechanism.
• Fixed-line (pre-cut) head: Uses individual short segments of line inserted directly into eyelets or clamps around the head. No winding required. Common on commercial and heavy-duty trimmers, and on brands like Husqvarna’s T25 head.

The sections below address each head type in order of prevalence. Jump to the section that matches your trimmer.

What Line Size Does My Weed Eater Need?

Using the wrong diameter line is the most common cause of spool jams, line breakage, and head damage. Match line gauge to trimmer class before buying.

Line Diameter by Trimmer Class

The recommended line diameter for your specific model is printed on the spool housing, inside the head cover, or in the owner’s manual. When in doubt, consult the trimmer manufacturer’s documentation — Husqvarna, STIHL, and Oregon Products all publish gauge specifications by model. Never use a heavier gauge than the manufacturer allows; it overloads the motor and prevents the bump-feed mechanism from advancing line.

Line Shape

Round monofilament is standard and works with all head types. Twisted and serrated line cuts denser vegetation more efficiently but wears faster and is only recommended for heads and motors rated for it. Unless your manual specifies otherwise, use round line.

How Much Line to Cut

For a standard bump-feed spool: cut two equal lengths of 9 feet each (18 feet total), or one 18-foot strand for single-line spools. Some larger heads take up to 25 feet per strand. Check the spool housing for the maximum footage rating — overfilling causes line to fuse under heat friction.

How to Put Line in a Bump-Feed Weed Eater (Most Common Method)

Step 1 — Disconnect Power

Electric (corded) trimmer: Unplug the power cord from the outlet completely. Do not rely on the power switch alone.
Battery trimmer: Remove the battery pack from the trimmer body.
Gas trimmer: Pull the spark plug boot off the spark plug. This is the correct safety step for any gas-powered trimmer service — it prevents accidental engine firing. Do not skip this step.

Step 2 — Remove the Spool

1. Hold the trimmer head steady with one hand.
2. Press the tabs on both sides of the bump-feed head simultaneously and pull the spool cover downward. On some models, twist the bump knob counterclockwise to unthread it before the cover releases.
3. Lift out the inner spool. Note the retaining clip or spring placement before removing — photograph it if needed for reassembly reference.
4. Remove any remaining old line from the spool. Clean debris from the housing with a dry cloth.

Step 3 — Measure and Cut the Replacement Line

1. Cut two lengths of line at 9 feet each (or the footage rated on your spool).
2. Confirm the diameter matches the rating printed on the housing.

Step 4 — Anchor the First Line

1. Locate the anchor slot or center eyelet on the spool — a small notch or hole in the middle divider of the spool.
2. Fold the first length of line in half and hook the midpoint into the anchor notch, or insert one end into the center eyelet and pull until a few inches remain as a tail.

Step 5 — Wind the Line

1. Look for the winding direction arrow molded into the spool body. Wind in that direction only — reverse winding prevents bump-feed from releasing line.
2. Wind the line in tight, even, side-by-side rows. Do not overlap or crisscross layers; overlapping causes line to bind and fuse.
3. Stop winding when approximately 6 inches of line remain. Hook this tail into the holding notch on the spool rim to keep it from unwinding during reassembly.
4. Repeat for the second line on the opposite half of the spool (most bump-feed spools have two separate halves separated by a center flange).

Step 6 — Thread the Exit Eyelets

1. Hold the outer housing and locate the two line exit holes (eyelets) on opposite sides of the head.
2. Feed the free tail of each line through its corresponding eyelet from inside the housing outward.
3. Pull each tail through so approximately 5–6 inches of line extends outside the head.

Step 7 — Reassemble the Head

1. Press the spool into the housing, aligning the retaining tabs and spring correctly.
2. Snap the cover closed or thread the bump knob clockwise until it seats firmly.
3. Tug each line strand outward gently to confirm it is not bound inside the housing.

Step 8 — Test the Bump Feed

1. Reconnect power (plug in, reinstall battery, or reattach the spark plug boot).
2. Hold the trimmer at operating position and run it at full throttle for 3–5 seconds.
3. Tap the bump knob firmly against a hard surface. Each tap should advance approximately 1 inch of line.
4. If line does not advance, see the troubleshooting section below.

How to Replace Line in an Auto-Feed Weed Eater

Auto-feed heads use centrifugal tension rather than a bump knob to advance line. The winding process is the same as bump-feed, but two important differences apply:

• Do not over-wind. Auto-feed mechanisms rely on precise line tension. Winding beyond the spool’s rated capacity jams the centrifugal clutch and stops line feed entirely. Fill only to the MAX line marked on the spool or to the point where the spool still spins freely in the housing.
• Spring tension is critical. When reassembling, confirm the internal spring is seated correctly in its groove before snapping the cover. A displaced spring is the primary cause of auto-feed jams after reloading.

Many auto-feed trimmer manufacturers — including Ryobi and BLACK+DECKER — offer model-specific pre-wound spools designed to eliminate tension errors. These drop-in spools are covered in the pre-wound spool section below.

How to Replace Line in a Fixed-Line or Pre-Cut Head

Fixed-line heads take individual segments of pre-cut line rather than a continuous wound strand. The process is the fastest of the three methods.

1. Disconnect power using the appropriate method for your trimmer type.
2. Locate the line eyelets or clamp slots around the perimeter of the head — usually 2, 4, or 6 positions depending on the head.
3. Cut replacement segments to the length specified by the head manufacturer. For most fixed-line heads, segments range from 6 to 9 inches. Using the correct length is critical: too long causes the line to contact the guard and break immediately; too short leaves insufficient cutting reach.
4. Fold each segment in half and press the folded midpoint into the eyelet channel until both ends lock in place, or insert each end into a paired set of holes until the retaining clip grips the line.
5. Tug each segment outward firmly to confirm it is seated and will not pull free under load.
6. Reconnect power and run the trimmer briefly to confirm all segments spin correctly without contacting the guard.

Can you convert a fixed-line head to bump-feed? Yes, on most trimmers. Universal bump-feed replacement heads with the correct thread pitch (most common: M10 x 1.25 LH) thread directly onto the trimmer shaft. Verify shaft thread size in the owner’s manual before purchasing a replacement head.

How to Use a Pre-Wound Replacement Spool

Pre-wound spools are factory-wound replacement spools that drop into the existing head housing, eliminating manual winding. They are the fastest reload option and prevent winding-direction errors.

Installation Steps

1. Disconnect power.
2. Remove the spool cover and pull out the depleted spool.
3. Drop the pre-wound spool into the housing, aligning the center post and retaining tabs.
4. Thread the line tails through the exit eyelets.
5. Snap the cover closed and test as described in Step 8 above.

Brand Compatibility

Pre-wound spools are not universally interchangeable. Most are engineered for specific trimmer models or families. Weed Eater brand trimmers (now owned by Husqvarna) use spools specific to their head generation — verify the part number against your trimmer’s model number before purchasing. Ryobi, BLACK+DECKER, and Greenworks each use proprietary spool dimensions. Using a mismatched pre-wound spool results in loose seating, incorrect line exit alignment, or cover failure.

Cost Comparison

Pre-wound spools cost approximately 2–4 times more per reload than buying bulk monofilament line and winding manually. For infrequent residential users, the time savings justifies the cost. For users trimming weekly or running commercial-grade equipment, bulk line on a spool roll is the more economical choice.

Common Weed Eater Line Problems and How to Fix Them

Line Breaks Immediately After Reloading

Cause: Wrong diameter line for the head (too thin snaps under load), or line segments cut too long in a fixed-line head and contacting the blade guard.
Fix: Verify diameter against the spool housing spec. For fixed-line heads, trim each segment to the manufacturer’s specified length.

Bump-Feed Head Not Releasing Line

Cause: Line wound in the wrong direction, line overlapping and binding on the spool, or the bump knob not fully seated.
Fix: Remove the spool and rewind in the direction of the arrow marked on the spool. Wind in flat parallel rows, not overlapping layers. Confirm the bump knob threads fully clockwise before testing.

Line Fusing or Welding Together on the Spool

Cause: Heat buildup from friction between overlapping line layers during high-speed rotation. This is caused by overfilling the spool or crisscross winding. Manufacturer service documentation from sources including Oregon Products identifies spool overfilling as the primary fusing cause.
Fix: Remove fused line completely. Rewind with flat, non-overlapping rows and do not exceed the spool’s MAX fill line. Storing the trimmer in a cool location between uses reduces ambient heat that softens monofilament.

Line Feeds Out Too Fast

Cause: Auto-feed spring tension is incorrect after reassembly, or line diameter is too thin for the head (lighter line feeds more freely under centrifugal force).
Fix: Disassemble the head and confirm the internal spring is properly seated. Upgrade to the next line diameter if your trimmer model supports it.

Line Wound in the Wrong Direction — What Happens

Reverse-wound line binds against the bump-feed ratchet and will not advance regardless of how hard you tap the knob. The line may also coil back toward the head during operation and wrap around the shaft. Remove the spool and rewind in the correct direction. No permanent damage occurs from a single incorrect winding.

Frequently Asked Questions

How do I know which direction to wind trimmer line onto the spool?

The winding direction arrow is molded directly into the plastic face of the spool. It is typically marked with an arrow and the label “wind” or shown as a curved directional symbol. If the spool is worn and the arrow is no longer legible, check the inside of the head housing cover — many manufacturers stamp the winding direction there as well. When in doubt, consult the trimmer’s owner’s manual, which specifies clockwise or counterclockwise winding relative to the viewing angle stated.

Can I use any brand of trimmer line in my weed eater?

Yes, as long as the diameter matches the specification on your spool housing. Trimmer line is not brand-proprietary — it is commodity monofilament. What is brand-specific is the pre-wound spool housing itself. Buy bulk line in the correct diameter from any manufacturer (Oregon, Arnold, Husqvarna, or generic) and wind it manually onto your existing spool.

How often should I replace trimmer line?

Replace line when it becomes too short to reach the guard’s cutting aperture or when you notice the trimmer losing cutting efficiency despite adequate line length. For residential users trimming a standard lawn, one full spool reload typically lasts 1–3 mowing seasons. Heavy use against hard surfaces (concrete, fencing, gravel) wears line significantly faster and may require reloading every few sessions.

Why does my trimmer line keep coming out of the spool during use?

The line tail was not fully fed through the exit eyelet during reassembly, or the spool cover is not fully snapped closed, allowing the spool to shift. Disassemble the head, re-thread both line tails fully through the eyelets until they protrude 5–6 inches, and press the cover until both retaining tabs click audibly into place before restarting the trimmer.