How Do You Insert Trimmer Line? (Complete Step-by-Step Guide for Every Head Type)

Which Trimmer Head Type Do You Have?

Identify your head type before touching the line. Applying bump-feed winding steps to a fixed-line head — or vice versa — results in a jammed or non-advancing head.

• Bump-feed spool: The most common design. A plastic knob on the bottom of the head taps the ground to advance line. The head unscrews or unclips to reveal a removable spool you wind yourself. Found on most Husqvarna, EGO, Craftsman, and mid-range Ryobi models.
• Fixed-line head (Speed Feed / AutoCut style): No removable spool. Line threads directly through two eyelet holes on the outer head, then the head rotates to wind the line internally. Common on STIHL AutoCut heads and Husqvarna T35 heads. Increasingly standard on battery trimmers.
• Pre-wound drop-in spool: A sealed, pre-wound replacement cartridge. No winding required — swap old for new. Common on entry-level Ryobi, Black+Decker, and Worx trimmers.

How to confirm your type: Check the underside of the head for a spring-loaded bump knob (bump-feed), two small eyelet holes with no removable inner spool (fixed-line), or a brand logo on a sealed cartridge (pre-wound). Your owner’s manual lists the head model number; search that number to confirm.

Head type does not reliably correlate with power source. Bump-feed heads appear on both gas and battery trimmers. Fixed-line heads are increasingly common on battery models but also appear on gas units. Confirm visually rather than assuming by fuel type.

Choosing the Right Trimmer Line Before You Start

Using incompatible line diameter causes spool jamming, premature breakage, or motor strain. Check the spool housing or owner’s manual for the specified diameter; it is molded into the plastic on most spools.

Line Diameter Selection Table

Line Shape

• Round monofilament: Standard. Works in all head types. Quiet, widely available.
• Twisted or serrated: Cuts heavier vegetation more aggressively. Compatible with bump-feed and fixed-line heads that accept the specified diameter. Do not exceed the spool’s maximum diameter rating.
• Multi-sided (square, star): More cutting edges per rotation. Same diameter compatibility rules apply.

How Much Line to Cut

• Bump-feed spool (single-line): 15–25 feet per load, depending on spool capacity. Most residential spools hold 20 feet comfortably.
• Bump-feed spool (dual-line): Cut two pieces at 10–15 feet each, or one piece at 20–25 feet folded at the midpoint.
• Fixed-line head: Cut one piece at 10–16 feet (folded and threaded simultaneously through both eyelets).
• Pre-wound spool: No cutting — line is factory-loaded.

Overfilling a bump-feed spool causes line fusing. Underfilling causes frequent reloads. Stay within the spool’s marked fill line.

Safety Steps Before Handling the Trimmer Head

Complete these steps every time before touching the trimmer head. The head can spin for several seconds after power is cut.

1. Battery-powered trimmer: Power off the trimmer, then remove the battery pack completely before starting work.
2. Gas trimmer: Turn the engine off, then disconnect the spark plug wire and tuck it away from the plug terminal so the engine cannot fire accidentally.
3. Corded electric trimmer: Switch off and unplug from the outlet.
4. Wait for the head to come to a complete stop — do not touch a coasting head.
5. Wear cut-resistant gloves. Trimmer line under tension can snap and cause lacerations. Safety glasses protect against debris dislodged while removing the spool.

No special tools are required for most heads. Some gas trimmer arbor nuts require the tool supplied with the trimmer (typically a combination wrench or pin spanner) to prevent the head from rotating during removal.

How to Insert Trimmer Line in a Bump-Feed Spool

This is the most common method and the most detailed process. Read the direction-of-wind callout before winding — winding in the wrong direction is the single most frequent installation error and results in a head that refuses to advance line.

Step 1 — Remove the Bump Knob and Spool

1. Hold the trimmer head stationary with one hand.
2. Turn the bump knob to unscrew it. Thread direction varies by brand: most bump knobs unscrew counterclockwise (standard right-hand thread), but some gas trimmer heads — particularly older STIHL and some Husqvarna models — use a left-hand thread that unscrews clockwise. Check your manual. Forcing the wrong direction strips the arbor.
3. On trimmers with an arbor nut instead of a bump knob: use the supplied wrench or pin spanner to loosen the nut. Hold the head using the head-lock button if your trimmer has one.
4. Remove the bump knob or arbor nut, then lift out the inner spool. Note the spring position beneath the spool — it must return to the same orientation on reassembly.
5. Clean debris from the head housing and the spool channel before loading new line.

Step 2 — Anchor the Line in the Spool

1. For a single-line spool: push one end of the line into the small anchor hole or notch at the center of the spool until it seats firmly.
2. For a dual-line spool with a center divider: locate the two anchor holes, one on each side of the divider. Insert one end of each line piece (or both ends of a folded single piece) into each anchor hole. Pull snug.

Step 3 — Wind the Line

1. Wind the line in the direction of the arrow, keeping each wrap tight and parallel to the previous one. Loose or crossed wraps cause fusing and jams.
2. Do not overfill. Stop winding when the line reaches the spool’s fill indicator line, leaving approximately 6 inches of line free at the end.
3. For dual-line spools: wind both lines simultaneously in the same direction, keeping each strand on its own side of the center divider.
4. Secure the loose end(s) in the spool’s temporary holding notch so the line does not unravel during reassembly.

Step 4 — Thread the Exit Eyelets and Reassemble

1. Hold the head housing and locate the exit eyelets — the small metal or plastic grommets on the outer rim of the head through which line exits.
2. Feed the free end(s) of line through the eyelet(s) from inside the head outward. On dual-line heads, one line exits each eyelet directly opposite the other.
3. Lower the spool back into the head housing with the spring seated correctly beneath it.
4. Thread the bump knob back on. Use the same thread direction you used to remove it, in reverse. Hand-tighten firmly — do not over-torque.
5. Pull each line outward to release it from the temporary holding notch and confirm it moves freely.
6. Trim both lines to 4–6 inches from the head if excess extends beyond that. Most heads auto-trim to the blade on the guard during operation, but starting with excessive line overloads the motor momentarily.

How to Insert Trimmer Line in a Fixed-Line (Eyelet) Head

Fixed-line heads such as the STIHL AutoCut and Husqvarna T35 do not use a removable inner spool. The head does not need to be removed from the trimmer shaft for reloading.

1. Cut one piece of line to 10–16 feet (consult your head’s manual for the exact specification). Fold it at the exact midpoint to create two equal strands.
2. Locate the two eyelet holes on opposite sides of the head housing.
3. Insert the folded midpoint loop into one eyelet and push it through until both free ends emerge from the opposite eyelet, or insert both ends simultaneously into their respective eyelets and pull through until the midpoint loop is flush inside the head. The method varies slightly by brand — confirm with your manual.
4. Pull both free ends outward until approximately 5–6 inches extend from each eyelet.
5. Rotate the head in the direction indicated by the arrow on the head housing. The head’s internal mechanism winds the line automatically. Continue rotating until both lines are wound and only 5–6 inches remain extending from the eyelets.
6. No reassembly required. The head never opened.

Fixed-line heads require no bump-knob advancement. Line feeds only when reloaded manually using this process. Speed Feed-style heads (EGO, Husqvarna) may have a central spool that rotates when you push a button while manually turning — confirm the specific sequence in your head’s manual.

How to Replace a Pre-Wound Spool

Pre-wound spools are sealed cartridges. No winding is required, but spool compatibility is brand-specific — a Ryobi spool does not fit a Black+Decker head. Cross-compatibility charts are available from major retailers, but treat them as guidance only and verify against your trimmer’s model number.

1. Remove the cap by pressing the release tabs on the sides of the head and pulling the cap free, or by unscrewing it counterclockwise.
2. Lift out the depleted spool cartridge and discard it.
3. Drop the new pre-wound spool into the head housing. Align any keying tabs with the matching slots in the housing.
4. Feed both line ends through the exit eyelets.
5. Snap or screw the cap back on until it clicks into place.
6. Pull both lines outward to confirm they move freely.

Rewinding a pre-wound spool yourself is possible — treat it as a standard bump-feed spool once the cartridge shell is empty — but the spool’s small size limits capacity and the process is fiddly. Replacement cartridges are inexpensive enough that rewinding offers minimal cost savings.

Testing the Line Feed and Confirming Correct Installation

1. Reconnect the battery, plug in the cord, or reconnect the spark plug wire.
2. Hold the trimmer over open ground — not concrete — and run it briefly at full speed.
3. Confirm both lines rotate in a flat, even plane. If one line is significantly longer than the other, the spool loaded unevenly; reload.
4. On a bump-feed head: tap the bump knob firmly on the ground while the trimmer is running. The head should advance a short segment of line (typically 1–2 inches per bump). If it does not advance, see the troubleshooting section below.
5. During normal operation, 4–6 inches of line should extend from the head. The guard’s cutter blade trims excess automatically on most models.

Troubleshooting: Line Not Feeding, Line Fusing, and Other Common Problems

Line not feeding / bump knob not advancing line: The most common cause is winding in the wrong direction — the line locks against itself rather than advancing when the knob retracts. Remove the spool and rewind following the arrow direction. Secondary cause: overfilled spool. Packed line binds against the spool walls and cannot advance. Remove excess line so the spool sits below its fill line. Tertiary cause: the bump knob spring is missing or seated incorrectly, preventing the spool from retracting after each bump.

Line fusing / line welding together on the spool: Caused by heat buildup when wound line strands contact each other during high-speed rotation. Cross-winding (wrapping line diagonally rather than in parallel rows) dramatically accelerates fusing. Overfilling compounds it by reducing airflow around the spool. Wind in tight, parallel rows and stop at the fill line. In hot or humid conditions, store spare pre-wound line in a sealed bag in a cool location — dry, cool line is less prone to fusing on contact.

Line breaking immediately at the eyelet: The exit eyelet grommet is worn, cracked, or missing, creating a sharp metal edge that shears the line. Inspect the eyelets; replacement grommets are available for most head models at hardware stores. Also check that the line diameter does not exceed the eyelet’s rated size — oversized line binds at the eyelet and breaks under centrifugal stress.

Spool will not sit flat or snap back into the head: Debris in the head housing is preventing full seating. Clean the housing channel thoroughly. Also confirm the spring is correctly centered beneath the spool — a canted spring holds the spool at an angle. On dual-line spools, confirm that both line ends are routed through their respective eyelets before pressing the spool down; a line trapped beneath the spool prevents seating.

Line spinning but not cutting effectively: Line is too short — less than 3 inches extending from the head produces minimal centrifugal cutting force. Run a bump advance to extend more line, or reload if the spool is depleted. Also check that the line diameter matches the specification; undersize line flexes excessively and deflects from vegetation rather than cutting.

Frequently Asked Questions

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

An arrow is molded directly into the spool body. Wind the line in the direction that arrow points. If the arrow is worn off, check the head housing — a second arrow is usually molded there. Winding against the arrow direction causes the line to lock against itself and not advance when the bump knob is tapped.

Can I use any brand of trimmer line as long as the diameter matches?

Diameter and shape compatibility matters more than brand. Any round monofilament line at the correct diameter (listed on the spool housing or in the owner’s manual) will function in a bump-feed or fixed-line head. Pre-wound replacement spool cartridges are the exception — those are brand-specific and in most cases model-specific. Verify compatibility against your trimmer’s model number, not just the brand.

Why does my trimmer line keep breaking right away after I reload it?

The most likely causes are a worn exit eyelet grommet creating a sharp shear edge, a line diameter that exceeds the eyelet’s rated size, or line that has become brittle from UV exposure or age. Replace cracked grommets, confirm diameter matches the spool spec, and use fresh line stored away from direct sunlight. Old, dry line snaps under centrifugal load even when correctly installed.

Do I have to remove the trimmer head to replace the line?

For bump-feed spools: you remove the bump knob and inner spool, but the head itself stays on the shaft. For fixed-line heads: the head stays on the shaft entirely — line threads directly through the eyelets without disassembly. For pre-wound drop-in spools: only the outer cap is removed; the head stays mounted. Full head removal from the shaft is only needed if the head itself is damaged or being replaced.