Guide
Strimmer line sizes and shapes explained
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In short
Strimmer line is sold by diameter, typically from 1.2 mm for light electric trimmers to 2.4 mm or more for powerful battery and petrol machines. Always use the diameter your manual specifies. Within that size, round line feeds easily and suits lawn edges, while twisted, square or star shaped line cuts tougher grass more aggressively.
Products for this job
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Strimmer line, also called cord, wire or string, looks simple, but the wrong type causes most strimmer frustrations: line that will not feed, snaps constantly or wears away in minutes. The right choice depends on what your strimmer head is designed for and what you cut. This explainer covers diameters, shapes and materials, and how to find what fits your machine.
Line diameter
Diameter is the most important figure, and your strimmer head is designed for a specific range. Thicker line is tougher and cuts heavier growth, but it needs more power to spin and may not fit the eyelets or spool of a light trimmer.
| Diameter | Typical use |
|---|---|
| 1.2 mm to 1.6 mm | Light corded and 18 V trimmers, lawn edges |
| 1.65 mm to 2.0 mm | Mid range battery trimmers, general garden use |
| 2.0 mm to 2.4 mm | High voltage battery and petrol strimmers, longer grass |
| 2.7 mm and above | Powerful petrol strimmers and brush cutters, rough ground |
How to find what your strimmer takes
The manual lists the line diameter, and it is often printed on the head or the spool too. Some Greenworks kits, for example, state 1.65 mm double line in the listing. If you are unsure, take the old line to a shop or measure it with a vernier calliper. Using thicker line than recommended can jam the head, overload the motor and reduce battery life.
Line shapes
Within the right diameter, shape changes how the line cuts and wears. Round line is the most common and feeds smoothly. Shaped lines have edges that slice rather than tear.
| Shape | Strengths | Best for |
|---|---|---|
| Round | Feeds easily, durable, low noise | Lawn edges, general trimming |
| Twisted | Quieter than square, more cutting edge | Mixed garden use |
| Square or star | Sharp edges cut thick grass well | Long, tough grass and weeds |
| Serrated | Aggressive cut | Rough growth |
Materials and quality
Most line is nylon. Better lines add reinforcement or a core to resist snapping and welding together in the spool. Cheap line can become brittle quickly, especially if stored in sunlight or a hot shed. Keep spare line in a cool, dark place in its bag. Brittle line snaps more often and is a common reason for frequent stops.
Single line, dual line and pre-wound spools
Single line heads have one line coming out of one eyelet. Dual line heads have two, which balances the head and cuts faster. Many battery strimmers use pre-wound spools made for that model, which are quick to swap but specific to the brand. Line on a reel is cheaper per metre and can be wound onto most refillable spools if the diameter matches.
Are strimmer heads and spools universal?
No. Spools and heads are usually brand and often model specific, because the fittings, thread and size vary. Universal heads exist, but check the thread size, direction and fitting carefully. Line diameter is the only part that is standardised. If you are choosing a new strimmer, our cordless strimmer guide notes head types such as EGO's Powerload.
Choosing line for your garden
Match the line to the job within the size your head allows. For a tidy lawn with edges, plain round line in the recommended diameter is ideal. For long grass, use a shaped line at the upper end of the recommended range. For brambles and woody growth, line is the wrong tool; a brush cutter with a blade is better.
Line and battery life
Thicker and shaped lines create more drag, which uses more battery. If your cordless strimmer runs out of charge quickly, check you are using the recommended diameter and that the line lengths are trimmed to the guard's cutter. Line that is too long overloads the motor, which is why the cutter blade on the guard is there.
If you also need a mower, a matched mower and strimmer set shares batteries between the two tools.
Frequently asked questions
What size strimmer line do I need? The size in your manual. Most garden battery strimmers take between 1.6 mm and 2.4 mm.
Can I use thicker strimmer line? Not beyond the maker's range. It can jam the head and strain the motor.
Is square strimmer line better than round? Square line cuts tough grass better; round line feeds more smoothly and lasts longer on edges.
Does strimmer line go off? It can become brittle with age, heat and sunlight. Store it somewhere cool and dark.
What you need
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Greenworks 40V 33 cm with edger wheel
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Ryobi ONE+ 33 cm mower + OLT1832 trimmer, 5 Ah