Maintenance procedure · Written to ASD-STE100 Issue 9 · Formatted to ANSI Z535

String Trimmer Line Replacement

Battery and corded electric trimmers with a spool head — taking the power source off first, reading the line size off the head, winding the spool the way the arrow says, and what to do when the head still will not feed
ApplicabilityBattery-powered and corded electric string trimmers with a replaceable spool in the trimmer head, bump-feed or automatic-feed. Not for trimmers with an engine.
Task time24 min to 39 min editorial estimate, not a measurement
PersonnelOne
Revisionv1 · 2026-07-29
BEFORE YOU BEGIN

Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.

Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.

Summary

Refilling a trimmer head is a ten-minute job that goes wrong for one reason more than any other: the line is the wrong thickness. Line size is not a property of string trimmers in general, it is a property of your particular head, and the makers do not agree because they are not describing the same part. Toro specifies .065 in (1.65 mm) and only that for the 51480 electric trimmer. EGO specifies 0.095 in (2.4 mm) for the ST1620T. A Husqvarna RapidReplace head will take anything from .065 in to .105 in. Those are three different heads, not three opinions about one number.

So this page will not tell you what diameter to buy. It tells you where the number lives — on the head itself, on the instruction card that came with it, or in your manual — and STIHL says the same thing in its own words: not all their line fits all their heads, so read the card for the head. What the page does give you is the sequence: power source off before anything opens, the spool out and cleaned, the line wound the way the arrow on the spool points, and a test with eye protection on. It also covers the part people skip, which is what to check when the new line still will not come out of the head.

Necessary equipment

ItemNote
Heavy glovesThe blade on the guard is sharp. Wear gloves near the guard.
Eye protectionWear eye protection for the test of the trimmer.
The manufacturer documentation for your trimmerThe documentation gives the line diameter and the line length for your head.
Scissors optionalUse scissors to cut the new line to length.
Small brush optionalUse a brush to remove grass from the trimmer head.
New trimmer line materialUse only line with the diameter in the manufacturer documentation.
New spool materialUse a new spool if the old spool has cracks.

Find the correct line for your head

Estimated 7 min to 20 min

NOTEThe line size belongs to the head and not to the machine. Find it before you buy line.
Cutting line diameter
Unverified — do not rely on this value
CONSULT THE MANUFACTURER DOCUMENTATION FOR YOUR TRIMMER HEAD. THE DIAMETER IS USUALLY MARKED ON THE HEAD ITSELF.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

Cutting line length for one spool
Unverified — do not rely on this value
CONSULT THE MANUFACTURER DOCUMENTATION FOR YOUR TRIMMER HEAD. EVERY HEAD HOLDS A DIFFERENT LENGTH.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

  1. Read the label on the trimmer head.
    • Most heads carry the line diameter on the head or on the cap.
    • The label is the fastest place to find the value.
    1m
  2. If the head has no label, read the manufacturer documentation for your trimmer.
    • STIHL tells you to read the instruction card for the head.
    • STIHL says that not all of its line fits all of its heads.
    3m
  3. Make a record of the line diameter and the line length.
    • You need the two values each time you fill the head.
    <1m
WARNING

USE ONLY NON-METALLIC LINE FROM THE MANUFACTURER.
A metal-reinforced line can break. A piece can leave the guard at speed and injure a person.

NOTICE

DO NOT USE LINE WITH A LARGER DIAMETER THAN THE MANUFACTURER GIVES.
A large diameter increases the load on the motor. The motor can become too hot and fail.

  1. Find a line with the diameter from the manufacturer documentation.
    • EGO tells you to use nylon line for its trimmers.
    • Toro tells you to use no other gauge of line for the 51480 trimmer.
    1m
  2. Cut the new line to the length from the manufacturer documentation.
    • A spool holds a set length and no more.
    • Toro gives a different length from Husqvarna, because the two heads are different.
    1m

Remove the power source

Estimated 1 min

NOTEThe trimmer can start while your hand is on the head. Remove the power source first.
WARNING

REMOVE THE POWER SOURCE BEFORE YOU OPEN THE TRIMMER HEAD.
The trimmer can start without warning. The head can injure your hand.

  1. If the trimmer has a battery, remove the battery from the trimmer.
    • EGO tells you to remove the battery before all service work.
    • STIHL tells you to remove the battery before you open the head.
    <1m
  2. If the trimmer has a power cord, disconnect the plug from the receptacle.
    • Toro tells you to disconnect the plug before you make an adjustment.
    • Move the cord away from the trimmer.
    <1m
  3. Put the trimmer on the ground with the trimmer head up.
    <1m

Open the trimmer head

Estimated 5 min

WARNING

WEAR HEAVY GLOVES BEFORE YOU TOUCH THE GUARD.
The blade on the guard is sharp. The blade can cut your hand.

  1. Wear the heavy gloves.
    • The guard carries a small blade that cuts the line to length.
    <1m
  2. Push the tabs on the side of the trimmer head.
    • STIHL tells you to push two tabs on the side of the head.
    • Some caps turn instead. Read the manufacturer documentation if the cap stays closed.
    <1m
  3. Remove the cap from the trimmer head.
    • Keep the cap. You install it again at the end.
    <1m
  4. Remove the spool from the trimmer head.
    • Some heads have a spring below the spool.
    • Keep the spring. The spring makes the bump feed operate.
    <1m
  5. Remove all the old line from the spool.
    • Old line that stays on the spool causes a bad feed.
    1m
  6. Remove grass and dirt from the trimmer head.
    • STIHL tells you to clean grass, dirt and debris out of the head.
    • Use the small brush.
    2m
  7. Examine the spool and the eyelets for damage.
    • A worn eyelet cuts the new line.
    • Replace a spool that has cracks.
    1m

Put the new line on the spool

Estimated 5 min to 7 min

Winding direction on the spool
Unverified — do not rely on this value
READ THE ARROW MARKED ON THE SPOOL. NO GENERAL DIRECTION IS CORRECT FOR ALL SPOOLS.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

  1. Find the arrow on the spool.
    • Toro tells you to wind the line in the direction of the arrows on the spool.
    • The arrow is the only correct direction for that spool.
    <1m
  2. Put one end of the line into the hole in the spool.
    • A spool for two lines has two holes and a wall between the two sides.
    <1m
  3. Wind the line onto the spool in the direction of the arrow.
    • Keep the line tight.
    • Keep the layers flat.
    • Keep the layers close together.
    • A twist in the line is a cause of a bad feed. Husqvarna gives this cause.
    3m
  4. Stop before the line reaches the outer edge of the spool.
    • Toro tells you to keep a space between the line and the outside edge.
    • A full spool binds and does not feed.
    <1m
  5. Put each end of the line into a slot on the spool.
    • The slot holds the end while you install the spool.
    <1m

Close the trimmer head

Estimated 3 min

  1. Put the spool into the trimmer head.
    • Install the spring first if your head has one.
    <1m
  2. Put each end of the line through an eyelet.
    • STIHL tells you to feed the line through each eyelet on the two sides of the head.
    <1m
  3. Install the cap on the trimmer head.
    • Push the cap until it locks.
    <1m
  4. Pull each end of the line to release it from the slot.
    • STIHL tells you to pull the two ends to release the slack.
    <1m
  5. Make sure that the two ends have the same length.
    • Different lengths make the head unbalanced.
    <1m
  6. Make sure that no line is longer than the guard permits.
    • STIHL tells you to keep the line inside the length of the line limiter.
    • The blade on the guard cuts a long line to length at the first use.
    <1m

Do a test of the trimmer

Estimated 3 min

Length of line that may extend from the head
Unverified — do not rely on this value
CONSULT THE MANUFACTURER DOCUMENTATION. THE LINE LIMITER ON THE GUARD SETS IT ON MANY MACHINES.

No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.

WARNING

WEAR EYE PROTECTION BEFORE YOU DO A TEST OF THE TRIMMER.
The line throws dirt and small stones. Dirt and stones can injure your eyes.

  1. Wear the eye protection.
    <1m
  2. Install the battery, or connect the plug to the receptacle.
    • Do this only after you close the head.
    <1m
  3. Do a test of the trimmer in an open area.
    • Make sure that no other person is near.
    1m
  4. Make sure that the line extends from the head.
    • A bump-feed head feeds the line when you touch the head on the ground.
    • An automatic head feeds the line at each start.
    <1m
  5. If the line does not extend, remove the power source again.
    <1m
  6. Examine the spool for a twist in the line and for a large diameter.
    • Husqvarna gives a twisted line as a cause of a bad feed.
    • EGO gives a heavy line as a cause of a bad feed.
    • EGO also gives a short line and a split end as causes.
    1m

Terminology

This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.

trimmer line
Also called: weed eater string, weed wacker string, strimmer line, trimmer string, grass trimmer line, cutting line, nylon line, the string in a weed eater
string trimmer
Also called: weed eater, weed wacker, weedwhacker, weed whipper, strimmer, grass trimmer, line trimmer, edge trimmer
trimmer head
Also called: cutting head, bump head, spool head, string head, mowing head, the bit at the bottom that spins
spool
Also called: reel, bobbin, cartridge, the thing the string winds onto
eyelet
Also called: grommet, line exit hole, the hole the string comes out of

When to use a professional

Stop if your trimmer has an engine. This page gives no procedure for a machine with an engine. The isolation step is different, and the manufacturer gives it. Read the manufacturer documentation for your trimmer.

Stop if the trimmer head has cracks. Do not install new line in a head with cracks. EGO tells you to replace a damaged head immediately. A head that breaks at speed throws pieces. Speak to a service dealer.

Stop if the head turns after you release the trigger. This is a fault in the control of the machine. Do not use the trimmer. A service dealer must repair it.

Stop if the guard is not on the trimmer. Do not use the trimmer without the guard. The guard holds the blade that cuts the line to the correct length. It also keeps stones away from you.

Stop if the motor becomes hot or slow with the new line. Remove the power source. Make sure that the line diameter agrees with the manufacturer documentation. Speak to a service dealer if the diameter is correct and the motor is still slow.

Stop if you cannot find the line diameter for your head. Do not use a diameter from a different machine. Speak to the manufacturer or to a dealer.

Common questions

What size trimmer line do I need?

Whatever your head is built for, and there is no way to answer it from a website. Toro specifies .065 in (1.65 mm) for the 51480 electric trimmer and says explicitly not to use any other gauge. EGO specifies 0.095 in (2.4 mm) for the ST1620T. A Husqvarna RapidReplace head accepts a whole range, .065 in to .105 in, and comes loaded with .095 in. That is a spread of well over half again from the thinnest to the thickest, across three ordinary consumer machines, which is why guessing is a genuinely bad idea. The number is normally moulded or printed on the head itself; if it is not, it is on the instruction card or in your manual.

Why won't my trimmer line feed?

Four causes come straight from the makers, and the first is by far the most common. EGO's own troubleshooting table lists heavy line — line thicker than the machine is rated for — as a cause, and the remedy is simply to go back to the specified diameter. Husqvarna lists line twisted around the spool, fixed by unwinding it and rewinding it properly. EGO also lists line that is too short and line with a split or bent end. Before you buy a new head, take the spool out and look at those four things.

Which way do I wind the line onto the spool?

The way the arrow on the spool points. Toro's instruction is to wind in the direction shown by the arrows on the spool, and that is the only rule that holds for every head, because the direction depends on which way that particular head turns. Wound backwards, the line will not feed and will often jam solid on the first bump. Look for the arrow before you start winding rather than after.

Can I use thicker line so it cuts through heavier weeds?

No, and this is the mistake that kills motors. EGO puts it plainly: heavier line than the manufacturer recommends increases the load on the motor and reduces its running speed, which results in overheating and damage to the trimmer. Toro says the same for its electric trimmer — a larger diameter string may cause the motor to overheat and fail. If you genuinely need to cut heavier growth, that is an argument for a bigger machine, not for stuffing bigger line into a small one.

Can I put wire or metal-reinforced line in it?

Never. EGO's warning is that metal-reinforced line, wire or rope can break off and become a dangerous projectile, and it repeats the point as an injury warning rather than a damage one. A trimmer head is a device for flinging whatever is in it at high speed, and nylon is chosen because it is survivable when it lets go. Metal is not.

Do I really have to take the battery out just to change the string?

Yes, and it takes two seconds. EGO's instruction is to remove the battery pack before servicing, cleaning, changing attachments or removing material from the unit, specifically to prevent accidental starting. STIHL says the same for the FSA 56: powered off and battery removed before the head is opened. Your hand goes inside the head during this job, right where the trigger would put it. A corded trimmer is the same argument with a plug instead of a battery.

Is a pre-wound spool worth buying instead of winding my own?

For most people, yes. A pre-wound spool from the maker removes the two things that go wrong — the wrong diameter and a bad wind — because the factory has already done both. Husqvarna's RapidReplace head is sold pre-loaded with 22 ft of .095 in line for exactly that reason. Bulk line is cheaper per foot and worth it if you use the machine a lot, but if you only trim a few times a season, the pre-wound spool is a reasonable thing to pay for.

Sources

Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.

  1. Tier 114in Electric Trimmer, Model No. 51480 — Operator's Manual (Form No. 3379-685 Rev B)The Toro Company · accessed 2026-07-29 · re-verification due 2027-01-25
  2. Tier 1Operator's Manual — 56-Volt Lithium-Ion Cordless 16in String Trimmer, Model ST1620T / ST1620T-FCChervon North America (EGO POWER+) · accessed 2026-07-29 · re-verification due 2027-01-25
  3. Tier 1Wind and Replace String Trimmer LineSTIHL Incorporated (STIHL USA) · accessed 2026-07-29 · re-verification due 2027-01-25
  4. Tier 1Trimmer Heads and Blades ReplacementSTIHL Incorporated (STIHL USA) · accessed 2026-07-29 · re-verification due 2027-01-25
  5. Tier 1RapidReplace trimmer head for high speed feedHusqvarna AB (Husqvarna US) · accessed 2026-07-29 · re-verification due 2027-01-25
  6. Tier 1Trimmer does not feed enough cutting line — Trimmer support, Help Center USHusqvarna AB (Husqvarna US Help Center) · accessed 2026-07-29 · re-verification due 2027-01-25

Revision history

Current version 1 · updated 2026-07-29 · next review due 2027-07-29

  1. v1 · 2026-07-29First draft. Scoped to battery and corded electric trimmers only: the isolation step is a battery or a plug, both of which Toro, EGO and STIHL publish, and the engine equivalent could only be sourced to a 2012 Husqvarna manual on an unstable download token, which is past the archaic-source threshold. Line diameter, spool length, winding direction and the maximum free line all publish as consult-manufacturer, because they are properties of the head. The spread across the three registered heads — Toro .065 in only, EGO 0.095 in, Husqvarna .065 in to .105 in — is published attributed in the summary and the FAQ and is deliberately not reconciled: those are three different parts, not three views of one number.

Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.

Comments and corrections

Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.

Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.

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