Unlike weak traditional monofilament line Aero-Flex Line Blades are engineered to lift air and grass for a clean cut with their sharper leading edges. The 4 powerful line blades hit and cut vegetation more frequently during each revolution. As an added bonus they cut and mulch at the same time. Also their more rigid design greater mass and twice the cutters means more grass cut per rotation to get the job done faster. Package is a mix of orange and yellow blades. Use two orange and two yellow for both clockwise or counterclockwise rotating trimmers.