Abstract: A grass cutting assembly for a rotary lawn mower having flexible resilient blades replaceably mounted on a rotor disc. Each elongated blade has an elongated inner end portion and a flat outer cutting portion which is twisted at 90.degree. to a flat mid portion. The lower surface of the rotary disc has a radial blade insertion groove which leads to a blade receiving opening which extends radially through each thicker blade holder portion which projects downwardly along the outer periphery of the disc. Each blade receiving opening has a vertically oriented narrow cylindrical portion adjacent the inner face whereby the blade rotates 90.degree. as it is inserted outwardly to a cutting position wherein the enlarged inner end abuts against the inner face of the blade holder portion, and mid portion is held in a vertical orientation and the outer cutting portion which projects beyond the outer periphery of the disc is held in a horizontal orientation.