Abstract: A lawn mower rotor assembly comprising a rotor body, filament cutting members, and a shear pin coupler, the rotor body being a flat star-shaped disk having five equally spaced arms projecting outwardly from the center of the rotor, each of the arms including near its outer periphery a lug for gripping one end of a short length of filament, the coupler being a disk fitting into a central counterbore in the rotary body having two cylindrical members projecting upwardly from the upper surface of the disk symmetrically positioned diametrically opposite from each other and mating with two recesses in the counterbore.