How Do You Change a Trimmer Line? (Step-by-Step Guide for All Head Types)

How to Change a Trimmer Line: Direct Answer and Overview

String trimmers (also called weed eaters, weed whackers, or line trimmers) cut grass and weeds with a rapidly spinning length of nylon line. Over time that line wears down, snaps, or runs out, and you will need to replace it. The process is not complicated, but it does vary depending on the type of trimmer head your machine uses. If you can identify your head type and follow the winding direction on the spool, you can complete the job in under ten minutes with no special tools.

This article explains the three main head designs, the specifications you need to check before buying or cutting line, and a detailed step-by-step process for each type. You will also find troubleshooting advice for common problems such as line that will not feed, tangling, and premature breakage.

Understanding Your Trimmer Head Type

Before you buy replacement line or remove anything from the machine, look at the trimmer head. Most residential string trimmers use one of three designs: bump-feed, tap-advance, or fixed-line. Each requires a different loading method, and confusing them is the most common cause of frustrating DIY repairs.

Bump-Feed (or Tap-Advance) Heads

Bump-feed heads hold a spool wound with a length of line. When the line wears short, you gently tap the head on the ground while the trimmer is running, which releases a small amount of new line. The centrifugal force of the spinning head then trims the line to the correct working length. Models with a small button or lever on the side of the head that advances line by hand are sometimes called tap-advance heads; the loading process is essentially identical. This is the most common head design on mid-range and premium gas, electric, and battery trimmers, and it offers the convenience of automatic line advancement.

Fixed-Line Heads

Fixed-line heads (also known as fixed-length or manual heads) do not hold a spool. Instead, they use one or two short, pre-cut pieces of line that lock into slots, holes, or tabs on the head. When the line wears down, you stop the trimmer, pull out the old piece, and insert a new one. These heads are simpler, cheaper, and very common on lightweight electric and battery trimmers. Some fixed heads accept a proprietary pre-cut cartridge; others simply take a measured length of bulk line that you thread through and lock in place.

How to Identify a Bump-Feed vs. Fixed-Line Head

• If the head has a visible spool cap that can be pressed in (often with release tabs), it is almost certainly a bump-feed or tap-advance design.
• If the head has no cap and instead has slots, holes, or notches holding short line ends, it is a fixed-line head.
• If the product page or manual mentions “automatic line feed,” “bump feed,” or “tap advance,” you have a spool-based head.
• If the manual says “replace the cutting line” without ever referring to a spool, you likely have a fixed-line head.

Gas vs. Electric vs. Battery Trimmers

Your trimmer’s power source does not change the fundamental reloading procedure, but it does affect safety. Gas trimmers must be turned off and allowed to cool, and the spark plug wire should be disconnected to prevent accidental starting while you work. Electric trimmers must be unplugged. Battery trimmers require removing the battery pack. The head designs can appear on any power type, so always identify the head first and then apply the appropriate safety step for your machine.

Key Factors to Consider Before Replacing the Line

Not all trimmer line is interchangeable. Using the wrong diameter can damage the engine or motor, reduce cutting performance, or cause the line to jam in the head. Check these three things before buying or cutting any line.

Match the Line Gauge (Diameter) to Your Trimmer

Trimmer line is sold by diameter, usually in thousandths of an inch. Common residential sizes range from about 0.065 inches (light duty) to 0.095 inches (standard), with heavy-duty lines at 0.105 inches, 0.110 inches, 0.130 inches, and even larger for professional units. The correct gauge depends on the power of your trimmer and the size of the eyelets on the spool or head.

You will find the recommended gauge stamped on the spool, printed in the manual, or listed on the original line packaging. If you cannot find it, measure the old line with a ruler or caliper, or bring the spool to a hardware store and compare diameters. Using line that is too thick may not fit through the eyelet, can overwork a small motor, and may make the line difficult to advance. Line that is too thin will cut poorly, break quickly, and may not engage the feed mechanism properly. When in doubt, choose a mid-range diameter such as 0.080 or 0.095 inches for a standard home trimmer, but prefer the manufacturer’s recommendation.

Line Length: How Much Do You Need?

The amount of line you need depends on the spool size. A typical residential bump-feed spool takes anywhere from 8 to 25 feet of line, and many manufacturers specify an exact length such as 15 feet. The old line you remove is your best guide: unwind it, keep the usable portion, and cut the new line to roughly the same length. For fixed-line heads, the requirement is much shorter — usually a single piece between 6 and 12 inches, or two pieces of about 8 to 10 inches each.

If you buy bulk line on a roll, you can cut it to size yourself. If you buy a pre-wound spool, it comes ready to install; you simply remove the old spool and drop in the new one, then thread the line ends through the eyelets. Pre-wound spools are convenient and are recommended for first-timers because they eliminate the risk of winding the line in the wrong direction.

Safety Steps Before You Start

• Disconnect power: remove the battery pack, unplug the cord, or disconnect the spark plug wire so the trimmer cannot start accidentally.
• Let the machine cool: especially with gas trimmers, the exhaust and head area can be hot.
• Wear gloves and eye protection: the head may have sharp edges, and old line can be brittle.
• Work on a clean, flat surface: small springs and washers inside the head are easy to lose in grass or gravel.
• Check for fuel leaks (gas models): if you smell fuel or see a leak, address it before tilting the trimmer, and never work near an open flame.

Step-by-Step Guide for Bump-Feed and Tap-Advance Heads

This is the most common procedure and applies to the vast majority of spool-based trimmers. The steps are nearly identical for bump-feed and tap-advance designs.

Step 1: Prepare the Trimmer

Set the trimmer on a flat work surface with the head facing up. Remove the battery, unplug the cord, or disconnect the spark plug wire. Wipe away any grass clippings and debris from the head using a stiff brush or cloth so you can see the cap and tabs clearly.

Step 2: Remove the Spool Cap and Spool

Look for the spool cap on the bottom of the head. Many caps have two recessed tabs or arrows on opposite sides. Press the tabs together (some caps require a coin or screwdriver in a slot) while pulling the cap straight off. In some designs, you press the cap inward and rotate it counterclockwise to unlock it. Once the cap is off, lift or slide out the spool. Take note of how the spool sits in the housing, including any washer, spring, or plastic insert. Lay the parts out in order so reassembly is straightforward.

Step 3: Remove Old Line and Inspect the Spool

Unwind and discard the old line. Check the spool for cracks, warped edges, or heavy wear; a damaged spool can cause tangling and uneven feed, and it is often worth replacing with a pre-wound spool or a factory part. Also inspect the spring and the eyelets on the head. Remove any bits of broken line stuck in the eyelets, because they will block the new line from feeding.

Step 4: Measure and Cut the New Line

Cut a single piece of bulk line to the length recommended by the manufacturer, or match the length of the old line. If no length is specified, a good starting point for a standard household spool is 15 feet. Keep the cut clean and square; a ragged cut can make threading difficult. If your spool has two line channels and two eyelets, you use one continuous length of line with both ends exiting the spool. If the head takes two separate pieces of line, cut two identical lengths.

Step 5: Thread the Line Through the Spool

Find the small anchor hole or groove on the spool. Insert the middle of the line into that anchor point (or push one end through a hole if the spool uses a single-end design). Then bring each end of the line out through the spool’s eyelets or notches. The spool body will usually have arrows or words such as “wind line here” indicating the correct path. Threading correctly at this stage prevents the line from slipping or tangling as you wind.

Step 6: Wind the Line Evenly in the Direction Indicated

Wind the line onto the spool in the direction shown by the arrows printed on the spool or the head. This is the single most important detail in the entire job — winding the wrong way is the top reason a newly loaded trimmer fails to feed. Keep light tension on the line as you wind, and lay the coils side by side in neat, tight rows from one side of the spool to the other. Avoid crossing the line over itself or leaving loose loops, because overlapping coils jam the feed mechanism. Leave a few inches of each line end protruding outside the spool’s eyelets.

Step 7: Secure the Line Ends

Most spools have small notches or slots at the outer edge that hold the line ends temporarily. Press each end into its notch so the line does not unwind while you reassemble the head. If there are no notches, hold the line ends in place with your thumb as you reinstall the spool.

Step 8: Reassemble the Head

Place the spool back into the housing, aligning any tabs or guides with the matching slots. Reinstall any washer or spring you removed earlier. Press the spool in until it clicks or locks, then replace the cap by aligning the tabs with the corresponding openings and pushing firmly until it snaps into place. Thread the line ends through the eyelets on the outside of the head. Give the line a light pull to confirm both ends move freely, then give each end a short, sharp tug to make sure it is seated.

Step 9: Test and Trim to Length

Reconnect the power, hold the trimmer away from your body, and start it. Let the head spin for a few seconds. The line will automatically trim down to the correct working length as it contacts the guard’s cutting blade. If the line is too long at startup, run the trimmer close to the ground or against the guard briefly. Do not try to trim the line to length with scissors while the machine is running.

Step-by-Step Guide for Fixed-Line Heads

Fixed-line heads are simpler and do not involve winding a spool. The exact mechanism varies slightly by model, but the general process is always the same.

Step 1: Disconnect Power and Remove the Old Line

Turn off the trimmer and remove the battery, unplug the cord, or disconnect the spark plug wire. Inspect the head to see how the current line is held. In most designs, the line is visible in a slot or hole around the perimeter. Pull the old line out, or press the release tab if your head has one. If the line is broken off flush with the head, use a small screwdriver or pliers to pull out the remainder.

Step 2: Measure and Cut the New Line

Check the manual for the recommended gauge and length, or measure the slot depth and the old line. Typically you will need one piece of about 10 to 12 inches or two pieces of about 8 to 10 inches. Use the correct diameter line; fixed heads have no spool to compensate for an oversized line, so gauge matching matters even more. Cut the line straight across with sharp scissors or a utility knife.

Step 3: Insert the Line into the Head

Slide one end of the line into the slot, hole, or channel until it seats against an internal stop. Some heads require you to feed the line through a hole on one side, around an internal groove, and out the opposite side. If the head uses two pieces of line, insert one into each channel, making sure both are seated fully and evenly.

Step 4: Secure and Reassemble

Depending on the design, you may need to close a locking tab, snap a cover back into place, or simply rely on the friction fit of the slot. If the head has a cover or cartridge, press it back on until it clicks. Give the line a light tug to confirm it is locked and will not pull out under centrifugal force.

Step 5: Test

Reconnect power and run the trimmer briefly. The line should stay in place and rotate with the head. If it flew out on startup, the line was not seated or the diameter is too small for the slot.

Troubleshooting and Maintenance Tips

Even with a perfect reload, trimmers can misbehave. Here are the most common issues and how to fix them.

Line Won’t Feed or Advance

• Wrong winding direction: rewind the spool following the arrow direction exactly. This is the most frequent cause.
• Line too long or too thick: the line may bind in the eyelet. Check the gauge and shorten the line.
• Line ends not threaded through the eyelets: both ends must exit the head freely; if one is trapped inside, nothing will feed.
• Tangled inside the spool: unwind and rewind with even, side-by-side coils under light tension.
• Worn spring or spool: if the head worked for a season and then stopped feeding, inspect and replace the spring or spool.

Line Keeps Breaking or Wearing Out Fast

• Line hitting hard surfaces: trimmer line is meant for grass and weeds. Striking concrete, stone edging, or fences shreds line quickly.
• Line too thin for the job: upgrade to the next larger gauge if your trimmer supports it.
• Line old or brittle: expose nylon line to sun and heat and it becomes brittle. Store bulk line in a cool, dark place.
• Throttle constantly at full speed: running at wide-open throttle on light weeds shortens line life; use a lower speed when possible.

Line Tangles or Birds-Nests Inside the Head

• Wind more slowly and keep tension on the line.
• Never overlap coils; fill the spool evenly in a single layer.
• Do not overfill the spool — leave the manufacturer-specified amount of line protruding.
• Remove debris from the eyelets regularly; grass packed into the eyelets can drag line back inside.

When Should You Replace the Whole Spool Instead of Just the Line?

Replace the entire spool when the plastic is cracked, the flanges are chipped, the center hub is worn, or the locking tabs no longer hold securely. A damaged spool will cause recurring tangles no matter how carefully you wind. Pre-wound spare spools are a good investment because they combine a new spool with correctly sized, correctly wound line and install in seconds.

Maintenance Tips for Longer Line Life

• Keep the head and eyelets clean of packed grass after every use.
• Store the trimmer indoors or under cover; ultraviolet light degrades both the line and the plastic head.
• Use the guard’s built-in cutter to keep line at the correct length instead of running the head against pavement.
• Buy line from a reputable brand and check the diameter marking on the packaging before purchase.

Frequently Asked Questions

How often should I change or replace the trimmer line?

There is no fixed schedule. Replace the line when it becomes shorter than the usable working length, snaps repeatedly, or stops feeding properly. Many homeowners reload once or twice per season, while those trimming large or rough areas may reload monthly. Keeping a spare pre-wound spool on hand makes the swap a two-minute job.

What happens if I use the wrong line gauge or diameter?

Line that is too thick may not fit through the eyelets, can jam the feed mechanism, and can strain the motor or engine. Line that is too thin cuts poorly, breaks quickly, and may not engage the bump or tap mechanism correctly. Always use the gauge marked on your spool or specified in the manual; typical residential sizes range from about 0.065 to 0.110 inches.

Do I have to wind the line in a specific direction?

Yes. The direction is marked with an arrow on the spool and often on the head housing as well. Winding the line in the opposite direction is the most common cause of a newly loaded trimmer that will not feed line. Follow the arrow, and keep the coils neat and even.

Can I use any brand of trimmer line, or do I need the OEM line?

You do not need to buy the manufacturer’s branded line. Any quality trimmer line of the correct diameter and length will work, provided it is compatible with your head type (spool-based vs. fixed-line). Keep the gauge within the range specified by the trimmer manufacturer, and you can safely choose between round, twisted, or serrated (star-shaped) line profiles depending on your cutting preferences and the density of the weeds you trim.