A string trimmer is a handheld cutter that spins a length of nylon line fast enough to slice grass and soft weeds where a mower cannot go. It handles fence lines, tree bases, deck edges and the strip beside a path, and many people call it a weed eater. I trim the strips under my orchard rows every season, and before I squeeze the trigger I check where the line will land, because it cuts whatever it touches, including bark and drip tubing. Below you get the parts, the power types, what the tool cuts, what to keep it away from and the gear to wear.
What Is a String Trimmer and What Does It Do?
The tool is a power unit on one end of a shaft and a spinning head on the other. The head holds nylon line that sticks out on both sides. Everything else on the machine exists to power, aim or guard that line. My guide on how a string trimmer works walks through the head, the line and the drive in more detail.
The Parts You Can See
Five parts carry most of what you need to know when you pick one up in a store or read a manual.
- Power unit: an electric motor fed by a battery or a cord, or a small gas engine. My guide to brushless and brushed string trimmers shows what the motor changes in use.
- Shaft: the tube that carries the drive down to the head. It is straight or curved, and some models fold or telescope. According to EGO, its folding model has a hinge that locks the two shaft sections and a clamp that sets the length. My guide to straight and curved shaft trimmers shows which shape fits which yard.
- Head: the housing that stores the line. On a bump head you tap the head on firm ground while it spins to release more line. An automatic head feeds line on its own, and Craftsman warns against bumping that kind of head.
- Line: the nylon cord that does the cutting. The maker sets the diameter for the motor. I explain how to choose the trimmer line size to use from your exact model’s manual.
- Guard: the shield behind the head. It carries a small steel blade that trims the line to length, and EGO says the machine must never run without it.
The head rules are opposite from one model to the next, so I follow the manual of the exact model I am holding. My guide to bump feed trimmers compares them with automatic feed heads.
How the Line Does the Cutting
The tip of that line does the cutting. According to EGO, you let the very tip cut, and cutting with more than the tip overloads the motor. Husqvarna says the same in other words: the end of the cord does the work, so you never press it into the area to be cut. Hold the line parallel to the ground and keep the head moving instead of leaning into the grass.
Weed Eater, Weed Wacker and Line Trimmer Are One Tool With Several Names
These names point at the same machine: a power unit, a shaft and a head with cutting line. Line trimmer and grass trimmer are plain terms. Manuals use string trimmer, grass trimmer or just trimmer for the same job, and the choice of word changes nothing about the tool. Weed Eater is a brand name, and Husqvarna now owns it.
A weed wacker is slang for that same line tool. A brush cutter looks similar but is a stronger machine that can also take a blade. Husqvarna allows grass blades and saw blades only on machines rated for them, with the correct handlebar, blade guard and harness. A trimmer with line only is a different tool, so I never fit a blade to one unless its manual lists that exact blade and guard. My guide to string trimmers and brush cutters explains which tool you need for which growth.
Blades Need a Rated Machine
Echo says never to install blades on its curved-shaft trimmers, and the Bosch GRT18V-40 and the EGO ST1610T forbid metal blades. Use only the cutting attachment and guard that the maker lists for your model.
How Battery, Corded and Gas String Trimmers Are Powered
The power source sets the weight, the noise and the upkeep. An electric string trimmer, whether battery or corded, and a gas model spin the same kind of line, so the choice comes down to where you work. Pick corded when an outlet reaches the whole job, battery when you want no cord or fuel and can recharge between jobs, and gas when the job is far from an outlet and you accept the mix, the noise and the exhaust. My guide to battery and gas string trimmers compares the two in detail.
| Type | What it needs | Maker figure | Main thing to watch |
|---|---|---|---|
| Battery (cordless) | A pack and charger the maker lists for that exact model | EGO lists operation at 32 to 104 F | Runtime depends on the pack, the speed setting and what you cut |
| Corded electric | A 120 V outlet and an outdoor-rated extension cord | One Greenworks manual lists 10 amps and 9.9 lb | An undersized extension cord drops voltage and power |
| Gas, two-stroke | Gasoline mixed with two-stroke oil | Echo lists 50:1 for the SRM-225 and its 21.2 cc engine | Mix, store and refuel as the manual says |
| Gas, four-stroke | Plain gasoline plus oil in the crankcase | Ryobi lists a 30 cc engine and no fuel mix | Check the oil level before each use |
Battery and Electric Models
A cordless string trimmer runs on a lithium-ion pack, so there is no cord to drag and no fuel to mix. The pack decides how long a job lasts. Makers give a low and a high speed setting, and Craftsman says the high setting shortens runtime. Voltage labels need care: Craftsman prints 20V Max for a pack whose nominal voltage is 18, so I never compare a Max number with a nominal number.
A battery powered string trimmer takes only the pack and charger the maker lists for that exact model, charged and stored within the temperature range in the manual, and never a damaged, modified or swollen pack. Before you service the head, switch the tool off, wait until the head has stopped, then take the pack out. A corded model skips the battery but ties you to an outlet, and you unplug it after the head has stopped and before you touch the head. I plan a battery job by the pack, because a pack that runs flat in the middle of a row means the row waits for the charger. My guide on corded vs battery string trimmers helps you choose by distance, run time and ground.
Gas Models
A gas powered string trimmer carries a small engine and a fuel tank. The two-stroke type needs a mix. Echo lists 50:1 for the 21.2 cc engine of its SRM-225, with oil that meets ISO-L-EGD or JASO FD, and Husqvarna lists 50:1 for the 25.4 cc engine of its 525LS. Use only the fuel, ratio and oil class in the manual of your exact model. The four-stroke type skips the mix but has an oil sump to check.
Gas costs you more in noise and exhaust. In NIOSH sampling of 80 landscaping workers, those using fuel-powered string trimmers, leaf blowers and chainsaws had significantly more noise and carbon monoxide exposure than those using battery versions (1). I treat any two-stroke fuel the same way: I measure the oil, label the can and mix a small batch. My comparison of 2-stroke and 4-stroke string trimmers explains what the engine type changes.
What a String Trimmer Cuts and What to Keep It Away From
It cuts grass, light weeds and similar growth at or around ground level. Greenworks describes exactly that in its manual, and EGO lists the edges of porches, fences and decks as its job, along with grass that a mower cannot reach. My picks of string trimmers for edging all have a real edge mode or an edger kit.
Jobs It Does Well
The jobs share one feature: a mower does not fit, or would scalp what it touches.
- Fence lines and posts: the line gets to the base of a post that a mower deck passes by.
- Deck, porch and wall edges: short grass along a hard edge.
- Corners and strips: places where the mower turns too wide.
- Tall grass: cut in layers from the top down, never straight to the ground.
EGO says to take off no more than 8 inches in each pass, because cutting tall grass at ground level wraps it round the head. Here is the arithmetic for one example:
- Start with grass 24 inches tall and trim the top 8 inches, leaving about 16.
- Trim the next 8 inches, leaving about 8.
- Trim the last 8 inches down to the height you want.
The same manual says to trim only when the grass and weeds are dry. I cut the tall growth at the hedgerow base in layers, since going straight to the ground is how the head ends up wrapped. My roundup of string trimmers for tall grass covers models for overgrown ground.
What to Keep It Away From
The line cuts whatever it reaches, so the list of things to avoid is longer than the list of jobs.
- Hedges, shrubs, flowers and compost: Greenworks says you cannot use the machine to cut or chop them. My hedge trimmer and string trimmer comparison explains which tool suits grass and which suits hedge growth.
- Tree bark and fences: EGO warns that the line damages tree bark, wood moldings, siding and fence posts.
- Hidden wiring and power lines: Bosch says never to cut near power lines or electric cords.
- Woody stems and saplings: this is brush cutter work, with a rated blade and harness.
The apricot and plum trunks I planted in 2016 still have thin bark at the base, so I keep the head away from them and finish the last inches by hand. Before I trim a tree strip I walk it and lift the drip tubing out of the way. Along the gravel yard I trim only the grass side of the edge, because the line throws stones.
Only Nylon Line
EGO says never to use metal-reinforced line, wire or rope, because it can break off and become a dangerous projectile. Use the maker’s line at the diameter the manual allows.
How to Read a String Trimmer Spec Sheet
Five numbers decide whether a model fits your yard: cutting swath, line diameter, head type, weight and, on battery models, the pack. The figures below come from maker manuals and show how far models differ. My top string trimmer picks apply these five numbers to specific models.
| Spec | What it tells you | Examples |
|---|---|---|
| Cutting swath | The width of the circle the line draws | EGO lists 16 in for one battery model, Craftsman 13 in, Greenworks 18 in for a corded one |
| Line diameter | The line the motor is built for | EGO lists 0.095 in, Craftsman 0.065 in round line, Echo 0.080 or 0.095 in |
| Head type | How line is released | Bump feed or automatic feed. Power winding, such as EGO’s POWERLOAD, is a separate feature that loads new line |
| Weight | What you carry through a job | Greenworks lists 9.9 lb for a corded model; Husqvarna lists 10.8 lb for a gas model |
| Runtime | How long a battery model works | Maker figures change with the pack and mode, so compare like with like |
Cutting Swath and Line Size
A wider swath cuts more grass per pass, but swath is only the nominal width of the circle the line draws at its proper length. What suits you also depends on the line and head the model allows and on its power source. The line size is a hard limit. Craftsman says serrated or heavier line overloads its motor and causes overheating, and EGO and Husqvarna tie extra line to motor strain. Use the string trimmer line the manual names for your head. My guide to string trimmer cutting width matches swath to yard size.
Weight, Shaft and Balance
Check whether the weight includes the battery or the fuel, since makers do not all count the same things. Echo, for one, lists a dry weight without the cutter head. A trimmer that feels light in the first five minutes feels different at the end of a long edge. My list of lightweight string trimmers compares seven models by stated weight.
Hands feel a trimmer too. In a laboratory test, a grass trimmer gave gloved-hand vibration of 3.5 to 5.8 m/s2, against 1.1 to 2.0 for a backpack blower, and it gave the highest exposure of the tools tested (2). Echo advises gloves, warm hands and breaks. I put gloves on before a long run along the ditch bank and keep them on.
Safety Gear and Habits Before You Pull the Trigger
Thrown objects are the main hazard. A US study of emergency department data estimated 81,907 lawn trimmer injuries from 2000 to 2009, and the eye accounted for 42.5% of them, mostly from foreign objects (3). Published eye trauma cases include bystanders as well as operators (4). Put on the gear first, then pick up the tool.
What to Wear
- Eyes: protection marked ANSI Z87.1. Greenworks says everyday glasses are not safety glasses, and Husqvarna wants goggles under a visor.
- Ears: hearing protection. Two petrol trimmer engines measured about 100 and 105 dB(A) at the operator, above the recommended limits for an 8-hour day (5).
- Legs and feet: long pants and sturdy boots with non-slip soles. Echo says not to wear shorts.
- Hands: gloves, which help against blisters and vibration.
Face protection alone is not enough. Seven motorized brush-cutting patients, mostly wearing nylon mesh face protection, still had penetrating eye injuries from objects 1 to 4 mm that came in from the side or through the mesh (6). I put on eye protection before I pick up the tool, not after it starts.
Distance, Guard and Stopping
Keep people and pets clear. EGO, Bosch, Echo, Ryobi and Milwaukee give 50 feet, and DeWalt and Craftsman give 100 feet. Stop the tool when someone comes closer. The guard stays on, and you never run a trimmer with a broken guard or spool.
- Switch the tool off.
- Wait until the head has stopped turning, and on a gas model let the engine cool.
- Take out the battery, pull the spark plug wire on a gas model or unplug a corded one, before you touch anything.
- Then clear the head, change the line or clean the tool.
EGO notes that a battery tool is always in operating condition until the pack is out, so I switch off, wait for the head to stop and take the battery out before I touch the head, even for a quick clear.
Fuel needs its own habits. Refuel with the engine off and cool, outdoors and away from flames, and move away from the fuel spot before you start, which Echo puts at 10 feet. A gas trimmer never runs in a shed or a garage, even with the door open. In EPA testing of gasoline lawn and garden engines including string trimmers, operators had short-term carbon monoxide exposures above 120 ppm for some equipment (7). My picks of gas string trimmers cover power, weight and warranty.
Where a String Trimmer Fits Next to Other Tools
This tool covers the places other tools skip, and it does not replace them. Each tool in the table has its own job.
| Tool | Best job | Limit to know |
|---|---|---|
| Mower | The open lawn | Cannot reach fence bases, posts or tight corners |
| String trimmer | Edges, corners and tall grass in layers | Stays off hedges, shrubs, bark and wiring |
| Edger | A clean vertical edge along a walk | Craftsman says its trimmer is not to be used to create trenches |
| Brush cutter | Woody growth and thick weeds | Needs a rated machine, blade guard and harness |
Some trimmers have an edging mode, and others forbid it. Milwaukee says not to tilt its trimmer to a right angle with the ground, and Craftsman says one of its models is not an edger, so I read the manual before I turn a head on its side. My guide to the string trimmer and edger split explains which tool does which job.
On my property the mower takes the alleys and the house lawn. The trimmer takes the tree strip edges, the fence lines and the hedgerow base. A brush cutter would come into play only for woody regrowth, and that is a different tool with its own gear. My guide to what a brush cutter is covers the parts, blades and safety rules.
Pick the Job First, Then the Power Source
My own tip is to walk the strip before each trim and pick up stones, tubing and anything the line could throw. Next, measure your longest job and the distance to the nearest outlet, match the power type to them, and read the manual of the model you are considering for its line size and head rules, because that manual decides what your string trimmer can safely do. My guide on what size trimmer you need matches swath, power and weight to your yard.
Frequently Asked Questions
What’s the difference between a weedeater and a string trimmer?
The difference between a weedeater and a string trimmer is mostly the name. String trimmer is the general term for a tool that cuts with spinning nylon line, while Weed Eater began as a brand name that many people now use for any such tool.
What do you use a string trimmer for?
You use a string trimmer to cut grass and light weeds in places a mower cannot reach, such as fence lines, posts, deck and porch edges and corners. It also trims tall grass when you cut it in layers from the top down. It is not for hedges, shrubs, flowers or woody stems.
What to use instead of a string trimmer?
Instead of a string trimmer, use a mower on open lawn, a dedicated edger for a clean edge along a walk, or a brush cutter with a rated blade for woody growth. Hand shears fit very small spots. Match the tool to the job and follow its manual.
Why is it called a weed eater?
It is called a weed eater because Weed Eater began as a brand name, and many people now use it for any string trimmer. The tool does not eat anything. The spinning line cuts the weeds off.
Does weed eater still exist?
Weed Eater still exists as a Husqvarna brand. Husqvarna announced in 2022 that it was reviving the name with a battery string trimmer, and it says it keeps supporting the green Weed Eater products.
References
- Alexander BM, Graydon PS, Pena M, Feng HA, Beamer BR. Hazardous exposures and engineering controls in the landscaping services industry. Journal of Occupational and Environmental Hygiene. 2025;22(3):189-202.
- Oh J, Chen N, Boyd C. Laboratory evaluation of occupational exposure to hand-arm vibration (HAV) during grounds maintenance equipment operations. Ann Agric Environ Med. 2023;30(2):384-389.
- Leinert J, Griffin R, Blackburn J, McGwin G. The epidemiology of lawn trimmer injuries in the United States: 2000-2009. J Safety Res. 2012;43(2):137-139. doi:10.1016/j.jsr.2012.03.001
- Lubniewski AJ, Olk RJ, Grand MG. Ocular dangers in the garden. A new menace: nylon line lawn trimmers. Ophthalmology. 1988;95(7):906-910. doi:10.1016/s0161-6420(88)33076-9
- Mallick Z, Badruddin IA, Khaleed Hussain MT, Salman Ahmed NJ, Kanesan J. Noise characteristics of grass-trimming machine engines and their effect on operators. Noise Health. 2009;11(43):98-102. doi:10.4103/1463-1741.50694
- Gau M, Meier P, Wiedemann P. Penetrating and perforating eye injuries with foreign bodies during motorized brush-cutting while wearing head protection gear [in German]. Klin Monbl Augenheilkd. 1999;215(5):311-314. doi:10.1055/s-2008-1034720
- Baldauf R, Fortune C, Weinstein J, Wheeler M, Blanchard F. Air contaminant exposures during the operation of lawn and garden equipment. J Expo Sci Environ Epidemiol. 2006;16(4):362-370. doi:10.1038/sj.jes.7500471
Safety Note: Read your manual first. A string trimmer or brush cutter throws debris with force, so clear stones, glass and wire from the area before you cut. Wear impact-rated eye protection with side coverage that meets ANSI Z87.1, hearing protection, gloves, heavy long pants, long sleeves and sturdy slip-resistant boots (steel-toe where your manual says so). Keep people and pets at least as far away as your manual says (50 feet in some manuals, 100 feet in others), and stop if anyone comes closer. Keep the correct guard fitted, use only the cutting attachments, handles and harness the maker approves for your exact tool, and never replace trimmer line with wire. A blade can kick sideways when it hits a stump or a thick stem, so fit the handlebar and harness your manual requires for blade work, hold both handles firmly and keep secure footing. Before you clear a jam, clean the tool or change line, a blade or an attachment, switch it off, wait for all movement to stop, then remove the battery, unplug the cord or disconnect the spark plug wire. Refuel a gas model outdoors with the engine off and cool, away from flames or sparks, and move away from the fueling spot before starting, as far as your manual says (often 10 to 30 feet); never run it in a garage, shed or other closed space. For a battery model, use only the maker’s battery and charger, charge it within the temperature range in your manual and never use a damaged or swollen pack. For a corded model, use a GFCI outlet, keep the cord clear of the cutting line and avoid wet conditions.