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HOW-TO GUIDEHow to Replace Strimmer Line: Bump Feed, Auto Feed and Fixed Head Spools
Replacing strimmer line means opening the head, winding fresh line onto the spool in the direction marked on it, threading the ends through the eyelets and clicking the cap back on. It takes about five minutes once you have done it once, and the only real trick is winding tightly in the right direction so the line does not tangle and jam.
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The trigger is easy to catch with a knee while you are crouched over the machine, so remove the battery, unplug the mains lead, or on a petrol model pull the spark plug cap off. Rest the strimmer so the head faces up, and let it cool if you have just been cutting, since a hot head softens the plastic cap and makes the tabs easier to break.
Work out which head you have
Almost every domestic strimmer uses one of three systems, and which one you own decides how you reload.
- Bump feed: a spool inside a cap you tap on the ground to release more line. Common on petrol and mid range cordless machines.
- Automatic feed: the head releases line on its own each time the motor slows or restarts. Common on lightweight electric strimmers.
- Fixed line or blade head: takes pre cut lengths or plastic blades that clip in individually, so no winding involved.
Fixed line heads are easiest: pull the old stub out, push a new pre cut piece in until it clicks, done. The rest of this guide covers spool heads.
Opening the head
Look for two tabs on opposite sides of the cap, squeeze both together and lift it off. Some heads use a central knob you unscrew instead, and a few older machines have a screw needing a Phillips driver. Note how the spool sits before you pull it out, and take a photo if there are springs or washers, because a bump feed head usually has a spring underneath that likes to escape. Strip off any leftover line and wipe the inside of the housing, since compacted grass and dried sap in there is a common reason line stops feeding smoothly.
Quick Tip
Keep a pre wound replacement spool for your exact model in the shed. When one runs out mid job you swap the whole cartridge in thirty seconds and rewind the empty one indoors, rather than kneeling on wet grass.
Getting the right line
Check the label on the strimmer or spool housing for the diameter. Light electric strimmers usually take 1.2mm to 1.6mm, mid range cordless machines 1.6mm to 2.0mm, and petrol brushcutters 2.4mm and up. Line thicker than the machine is rated for overloads the motor, will not feed through the eyelets cleanly, and drains a battery noticeably faster.
Round line is the default and copes well with soft grass. Twisted or square profile line cuts more aggressively through thick weeds, but it costs more and strains smaller motors.
Winding the spool
- Cut a length to suit your spool. Around 3 to 5 metres per side is typical, but if the spool has a fill line moulded into it, wind to that and no further. Overfilling is the most common cause of a head that will not feed.
- Find the arrow on the spool. There is nearly always a moulded arrow showing the winding direction, and going the wrong way means the line unwinds itself the moment the head spins.
- Anchor the line by hooking the end into the notch at the centre of the spool, or fold a double length in half and hook the loop over the divider on a twin chamber spool.
- Wind tightly in neat, flat layers, keeping tension with one hand as you turn the spool with the other. Loose or crossed windings pinch under load and jam the feed.
- Leave roughly 10 to 15cm free at each end and clip those ends into the retaining notches on the rim, which hold them while you refit everything.
Twin line versus single line spools
Twin line spools have a divider and two chambers, each with its own eyelet. Wind each half in the same direction, in its own chamber, and never let the two lengths cross the divider. Single line spools need the same care over direction and tension.
Refitting and testing
Thread the free ends through the eyelets from the inside out, drop the spool into place with the spring seated correctly, pull the ends free of the retaining notches and push the cap on until both tabs click. Give each line a firm tug: it should not pull out, but it should draw out a little when you bump the head.
Trim both lines to equal length. The guard usually has a small blade that does this on the first run, but matching them by eye first reduces vibration, and uneven lines are why a freshly loaded strimmer sometimes shakes badly. Refit the battery or plug in, hold the machine away from your legs and run it for a few seconds. If it vibrates hard or refuses to feed, open the head again. The cause is almost always overfilling, a crossed winding, or line wound against the arrow.
Making the new line last
Line left in a dry shed for years goes brittle and snaps constantly, so store spares in a sealed bag, and soak stiff line in water overnight to bring some flexibility back. Cut with the tip rather than burying the head in the grass, and keep clear of kerbs, fence posts and gravel.
How much strimmer line should I wind onto the spool?
Wind to the fill line moulded into the spool if there is one, otherwise roughly 3 to 5 metres per chamber. The wound line should sit below the rim, never proud of it, or it will rub on the housing and jam.
Can I use a different thickness of line than the manufacturer specifies?
Slightly thinner is usually harmless, though it breaks more often. Thicker is not recommended: it will not pass the eyelets cleanly, it loads the motor, and it cuts cordless runtime per charge.
Why does my new line jam straight after reloading?
Nearly always overfilling or a loose winding. Unwind everything and rewind tightly in flat layers following the arrow. Also check the eyelets are not worn into a sharp lip, which shreds line as it feeds.