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This accessory has flexible blades that cut with less effort yet are more landscape-friendly. Strimmer Brush Cutter Head

The string trimmer is both a blessing and a curse. It can be a tremendous labor-saving device that neatly tidies up shaggy grass along flower beds, around posts, and down the edge of sidewalks. But a string trimmer can also be a cranky nuisance when its line snaps or its head refuses to feed out more line. The Snap & Trim from Aero-Flex is an accessory that fits to a string trimmer and does away with trimmer line. The device is a shallow, dish-shaped holder with two flexible wing-like blades and a spinning glider disc that supports the trimmer head. In our test, we found that the device turns a string trimmer into a more precise and far more predictable tool, more like a mower. Installing the accessory on a trimmer is hassle-free and takes literally seconds.

In 1971, George Ballas—a Houston dance instructor and entrepreneur—founded Weed Eater, a company with one product, a power tool with a spinning flexible line head to trim tall grass and weeds. His initial prototype of the tool’s head consisted of a can of 3-Minute Pop Corn pierced with knotted pieces of heavy fishing line. You can have a look at it here. Ballas managed to rig the string-can setup to a rotary lawn edger and found that the prototype, crude as it was, was remarkably successful. He learned that a rapidly rotating line head could easily slice through grass and weeds. From there, he founded Weed Eater a company that still produces electric and gas-engine string trimmers. Although many people incorrectly refer to all string trimmers as Weed Eaters, it’s a specific model name and a trademark now owned by Husqvarna AB. (Weedwacker is a trademark owned by Stanley Black & Decker.) Today’s string trimmer, in all its permutations, has its origins in that primitive but effective prototype developed by Ballas in 1971.

To be sure, both electric and gas-engine string trimmers have their strengths, such as the ability to rapidly bring unruly borders areas under control. But they also have some weaknesses that are well known to anybody who has ever spent much time using them. One moment, it can be a loud-but-productive power tool slicing down grass and weeds where a mower can’t reach. The next moment, it can be temperamental nuisance. Its line may snap, and then the head will refuse to feed out more line. Or, with a moment’s inattention, those pieces of spinning line can strip the bark off a prized planting or gouge a fence post.

Because of the aforementioned problems, string trimmers need a cover that’s easily removable to deal with line replacement, to rewind snarled line, or to feed out fresh line after it’s snapped and the remaining stub has withdrawn inside the head. This tool-free access to the line spool makes it a natural candidate for a retrofit head of some kind. In most cases, removing the cover over the trimmer spool is tool free: Press in on the tabs holding the cover and remove it. Slide the spool of string off its shaft.

To install the Snap & Trim, snap its tabs into the same openings that the previous cover used. The device is designed to fit a wide range of consumer-grade trimmers. It will fit 51 models produced by Black & Decker and six by Craftsman—two of the most popular consumer brands.

We tried the device on a Craftsman CMCST910M1, a 20-volt 13-inch trimmer that operates at 5,500 to 7,200 rpm (those speeds are important, as we’ll explain in a minute). Replacing the Craftsman’s line head with the Snap & Trim took about 30 seconds, and the accessory improved the tool’s performance.

We found the Snap & Trim does provide a more precise and predictable cutting action than string, at least in our tests around a vinyl fence, edging a flower bed, and navigating around trees. The ball bearing-mounted glider disc below the blades allows you to rest the trimmer head on the lawn and skim along the surface. The benefit here is that the trimmer now functions more effectively as a specialized small-area mower, handling corners and slopes where it would be impractical or even impossible to cut with a mower. Another advantage of the technology is that the fluorescent color of the blades makes them far easier to see, even in bright sunlight. The spinning blades form a glowing circle that helps you see the area you’re trimming.

The blades wear away as you work; the more aggressively you use the trimmer, the sooner they’ll need replacing. To do that, press the Snap & Trim tabs and remove it, lift out the old blades, and slide in the new ones. The process, start to finish, takes a minute or less.

The flexible nylon polymer blades have a complex cross section somewhat like an airplane wing. And they’re dimpled like a golf ball to improve their aerodynamics (you can read more about the specifics of that feature at Scientific American’s excellent description here.)

Aero-Flex, the manufacturer, says that it undertook careful studies of materials and the aerodynamics of the blades to ensure the performance would be superior to that of trimmer string. Though the blades are highly flexible, their increased mass (compared to string) requires less rotational force and lower speed to accomplish the same amount of work. This means that you can run the trimmer at lower rpm, not only conserving battery life but also reducing noise and the likelihood of damage with an accidental strike to a surface like fencing or garage door trim. For those of you who are mathematically inclined, you can see the specific formulae that the manufacturer applied in designing its blades.

Suppose you want to try this technology but don’t have a Craftsman or Black & Decker trimmer? Aero-Flex makes a wide range of similar retrofit heads to fit just about any trimmer, whether powered by a gas engine or a battery.

Roy Berendsohn has worked for more than 25 years at Popular Mechanics, where he has written on carpentry, masonry, painting, plumbing, electrical, woodworking, blacksmithing, welding, lawn care, chainsaw use, and outdoor power equipment. When he’s not working on his own house, he volunteers with Sovereign Grace Church doing home repair for families in rural, suburban and urban locations throughout central and southern New Jersey.

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