Monofilament can also have a tough time getting through heavy

weeds, vines, and light brush. Engineers at Aero-Flex, Rock Hill, S.C. (aero-flex.com), took a new approach, designing an airfoilshaped Flexible Line Blade. Four such blades and a special hub, the Mach 4 Trimming System, replace round monofilament lines. The blade's shape reduces drag through air and grass, convertingwasted power into better cutting. The blades are also heavier, so they last up to 20 times as long as monofilament, and will let manufacturers build trimmers that operate at lower speeds, thus saving gas. Trimmers equipped with the cutting airfoils are also quieter and generate fewer emissions.