String trimmers differ mostly in how they are powered, what attachments they take, and the line and guard they use. This guide covers those choices with Ohio State University Extension’s guidance on handheld trimmers and brush cutters, one battery trimmer’s operator manual and the California Air Resources Board’s small off-road engine fact sheet.
How a string trimmer works
A string trimmer cuts grass and weeds by spinning a flexible nylon line at high speed. The tip of the line does the cutting, so keeping the line at the correct length matters for performance. According to the operator manual for one battery-powered model, the machine is equipped with a line cut-off blade on the guard that continuously trims the line to ensure a consistent and efficient cut diameter. When you hear the engine running faster than normal or trimming efficiency drops, you advance more line by tapping the trimmer head against the ground while the machine runs. The line is automatically released and the cut-off blade cuts the excess length.
Ohio State University Extension notes that handheld trimmers and brush cutters are capable of performing numerous tasks on small farms and gardens. While they are usually used for completing grass-trimming operations, many are designed to incorporate attachments such as brush-cutting blades, cultivators and edgers. They vary in size from small, handheld models to larger units with shoulder straps and handlebar controls.
Trimmers, brush cutters and attachments
Ohio State University Extension says many trimmers are designed to take attachments such as brush-cutting blades, cultivators and edgers, and that units range from small handheld models to larger ones with shoulder straps and handlebar controls. If you think you may want an edger or a brush blade later, check that the model you buy supports those attachments, and use them only as they were designed to be operated, as OSU advises. Our attachment-capable trimmer guide walks through multi-tool systems in more detail.
Power sources: gas, battery and corded
String trimmers come with gas engines, battery packs or a corded electric motor. For gas equipment, the California Air Resources Board (CARB) reports that small off-road engines in California are primarily used for lawn, garden and other small off-road equipment. As of 2021, 61% of California SORE are used in residential lawn and garden equipment. CARB also states that operating a commercial lawn mower for one hour emits as much smog-forming pollution as driving a new light-duty passenger car about 300 miles. While residential trimmers are smaller, the emissions add up across a neighborhood.
One 24V cordless model’s operator manual lists a cutting line diameter of 0.065 inches (1.65 mm) and a weight of 5.07 lbs (2.3 kg), figures that are specific to that model and not universal. Runtime depends on the battery capacity and the load. If you already own other cordless yard tools, staying on one battery platform can simplify charging and spare-battery logistics. Our battery platform guide explains how to think about compatibility across tools.
For a broader look at the trade-offs between power types, see battery vs gas vs corded garden tools.
Cutting line: diameter, shape and loading
The line does the work, so matching it to the trimmer and the job makes a difference. The operator manual for one battery trimmer specifies using only nylon cutting line of 0.065 inches (1.65 mm) diameter. That figure applies to that model. Other trimmers may require thicker or thinner line, and the owner’s manual is the place to check.
To replace the line on the example battery trimmer, the manual instructs cutting two pieces of cutting line approximately 3 meters long each, bending one end 1/4 of an inch (6.35 mm), placing the lines into the anchor holes of the spool, and winding them tightly in the indicated direction without going beyond the edge of the spool. The spool cover is then pushed until it clicks into position. For a deeper look at line types and loading methods, read our trimmer line guide.
Cutting head and guard
The guard, sometimes called the deflector, is a safety component, not an accessory. Ohio State University Extension says to verify that the shields and deflector guards are in place and that the safety features are not overridden. The guard also houses the line cut-off blade. On the battery trimmer described in the manual, the cut-off blade can be set to two positions: a 10-inch (254 mm) cutting diameter for greater runtime, or a 12-inch (305 mm) diameter for a larger cutting area. Changing the setting involves removing the battery pack, taking out the blade screws, turning the cut-off blade 180 degrees, and reinstalling the screws.
Safety gear and safe operation
Ohio State University Extension recommends several pieces of personal protective equipment when operating a string trimmer or brush cutter. Wear safety glasses with side shields or goggles to protect the face and eyes from flying debris. A face shield or screen over safety glasses provides additional protection. Ear protection preserves hearing from the high level of noise produced by the engine. Leather gloves protect hands from cuts, splinters, abrasions and contact with sharp cutting edges and flying debris. Sturdy leather work boots or hard-soled shoes protect ankles and feet from the rotating cutter head and flying debris, and steel-toed boots help provide additional protection. Pants and a snug-fitting long-sleeved shirt protect skin from flying debris and cuttings.
Before starting work, inspect the area where the equipment will be used and remove all visible stones, sticks, wires or other debris. Ohio State Extension advises placing the unit on the ground before starting it, not operating equipment in a closed building because poisonous gases (carbon monoxide) can build up quickly, and maintaining a firm grip on the handles while working slowly to minimize kickout and the risk of hitting hidden objects. Keep bystanders at least 50 feet away. Do not operate the equipment when fatigued or under the influence of drugs or alcohol, and operate only with adequate visibility and light.
Comparison: key factors to weigh
The table below summarizes the main choices. Model-specific numbers are labeled as such.
| Factor | What to consider | Source |
|---|---|---|
| Attachments | Check that the model takes the attachments you want (brush blades, cultivators, edgers) | Ohio State University Extension |
| Power source | Gas small off-road engines are regulated in California; check runtime, battery and line specs in the manual for battery models | CARB SORE fact sheet; battery trimmer operator manual |
| Cutting line diameter | Match the diameter specified in the owner’s manual (example model: 0.065 in / 1.65 mm) | Battery trimmer operator manual |
| Guard and cut-off blade | Must be in place; some guards allow switching cutting diameter (example model: 10 in or 12 in) | Ohio State University Extension; battery trimmer operator manual |
| Safety gear | Eye protection, ear protection, gloves, sturdy boots, long sleeves and pants | Ohio State University Extension |
| Emissions | Gas SORE already exceed light-duty passenger car smog-forming emissions in California; CARB sets standards and aims for zero-emission transition by 2035 where feasible | CARB SORE fact sheet |
Maintenance and storage
Ohio State University Extension advises keeping the equipment and all attachments in good repair and using the maintenance schedule provided in the owner’s manual, which is the best source of information regarding equipment maintenance. Always shut off the engine and disconnect the spark plug wire before performing maintenance or changing attachments. For gas models, maintain proper oil levels and lubrication of moving parts, replace brush-cutter blades when they are damaged or excessively dull, and drain the fuel tank in a safe area and run the engine on idle until it stops before storing the equipment for extended periods.
For the battery trimmer detailed in the operator manual, cleaning involves a moist cloth dipped in neutral detergent. Aggressive detergents or solvents should not be used on plastic parts or handles. The trimmer head should be kept free of grass, leaves or excessive grease, and air vents must stay clean and free of debris to avoid overheating and damage to the motor or the battery. Water should not be sprayed onto the motor and electrical components. Before transportation and storage, remove the battery pack. Keep the machine away from corrosive agents such as garden chemicals and de-icing salts, and store it where children cannot come near it. Our string trimmer maintenance guide covers head, guard and engine care in more depth.
Operating tips for clean cuts and fewer problems
The battery trimmer manual offers several troubleshooting pointers that double as good technique advice. Cut with the tip of the line and avoid stones, walls and other hard objects. Advance the cutting line regularly to keep full cutting width. When cutting tall grass, work from the top down if grass winds around the trimmer head and motor housing. If the motor is overloaded, remove the trimmer head from the grass. If the battery pack or machine becomes too hot, cool the machine for approximately 10 minutes and let the battery pack return to normal temperature.
Frequently asked questions
Can I use any diameter line in my trimmer?
No. The operator manual for one battery trimmer specifies using only nylon cutting line of 0.065 inches (1.65 mm) diameter. The manual’s troubleshooting table lists heavy cutting line as a cause of problems. Always check your owner’s manual for the correct diameter.
Do I really need to wear ear protection with a battery trimmer?
Ohio State University Extension recommends ear protection to preserve hearing and protect the ears from the high level of noise produced by the engine. OSU’s recommendation is written for string trimmers and brush cutters in general; follow the safety equipment list in your own model’s manual too.
How far should bystanders be from an operating trimmer?
Ohio State University Extension says to be aware of bystanders in the event of thrown objects and to allow at least 50 feet of safe distance.
Ready to compare models? Browse our string trimmers and edgers category for more guides.
