String trimmer vs brush cutter

These are not two grades of the same tool. A string head and a steel blade cut by different mechanisms, fail at different things and want different guards, and the published specifications make the trade unusually easy to see.

The short answer

Two different ways of cutting

• Line cuts by repeated impact. Monofilament spun fast enough severs soft tissue by hitting it thousands of times a minute. It is self-limiting: hit something too stiff and the line wears away instead of the stem.
• A blade cuts by shearing. RYOBI's reversible Tri-Arc is a three-point steel blade that slices through a woody stem in one pass, and reverses to use the second set of edges when the first dull.

That self-limiting property of line is a safety feature as much as a limitation. A blade does not have it.

The published figures

When string is the right answer

1. Grass along a path, a wall or a bed edge — the everyday job.
2. Tall soft weeds, where the wider path matters — see best trimmers for tall weeds.
3. Anywhere the tool will touch a fence, a post or a downspout and needs to forgive it.
4. Anywhere children, pets or windows are within throwing distance.

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When a blade earns its place

1. Woody stems that line frays against instead of cutting.
2. Neglected ground being brought back, where the material is brush rather than grass.
3. Repeated clearing where line consumption becomes the real cost — our trimmer line guide covers why heavy work eats line.

Before fitting one, read yard tool safety basics and confirm the guard your powerhead requires. Our brush cutter page covers the attachment in more detail.

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The safety difference, stated plainly

String is forgiving in a specific and useful way: it wears out against things it cannot cut. Hit a fence post with a string head and you lose line. Hit it with a steel blade and the blade deflects, which transmits that energy back up the shaft to you.

• Blade thrust. A spinning blade that catches a stiff stem can push the tool sideways with real force. This is a documented characteristic of bladed trimmers generally; RYOBI does not discuss it on the attachment product page.
• Thrown debris. A blade ejects cut material faster and further than line does, which is why blade work conventionally uses its own guard.
• The guard question is unanswered. RYOBI publishes no guard detail for the Tri-Arc, so confirm what ships with it and what your powerhead requires before fitting. That is not a hypothetical caution — it is a blank on the spec sheet.
• PPE changes. Eye protection is not optional with a blade, and our yard tool safety basics covers the rest.

Consumable cost runs the other way

That asymmetry is the practical argument for owning both heads on one powerhead rather than choosing between them: string for the weekly job, blade for the twice-a-year one, and one battery and motor serving both.

What sits between the two

There is a middle ground worth knowing about before you buy a blade. Heavier-gauge line in a bump head handles a surprising amount of what people reach for a blade to do — 0.095 inch line against soft woody growth is more capable than 0.080 inch, and our trimmer line guide covers where the gauge ceiling actually is.

Above that, and below a brush cutter, sits the job most people actually have: tall soft weeds rather than saplings. That is a string job with the right line, and it has its own page — best trimmers for tall weeds.

The powerhead decides whether you have the choice

Neither element matters if the tool will not take the other one. An attachment-capable powerhead lets one motor and one battery run a string head today and a blade next spring; a fixed-head trimmer locks you into string forever.

The Greenworks 2123802 publishes the broadest compatibility in our registry — Poulan Pro, RYOBI EXPAND-IT and TrimmerPlus — which is the practical reason to buy an attachment system at all.

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Which to buy, if you are buying one

Buy the string trimmer. Almost everyone reading this has a grass-and-weeds job, and string is wider, safer and better documented for it. Add the blade later, as an attachment on an attachment-capable powerhead, when you meet the material that defeats line — and you will know when that happens, because the line will fray against the stem instead of cutting it.

Buying a blade first, for a job you might have, means buying the narrower tool with the thinner spec sheet and the bigger safety envelope for a use case that has not arrived.

What we cannot tell you

We have not cut anything with either. RYOBI publishes no maximum stem diameter for the Tri-Arc blade, no weight, no guard specification and no warranty, so we cannot tell you where its limit is — only that it exists somewhere above where line stops working. Nobody publishes a cutting-rate comparison, so the pass arithmetic above is width only and ignores how much slower or faster each element travels through material.