A rotary mower includes a rotary cutting disk, at least one knife, at least one knife pin, and a spring plate. The rotary cutting disk has at least one knife mount location. Each knife has an end with an opening therein. Each knife opening has a double keyhole shape with a larger center hole and two smaller partial holes respectively on generally opposite sides of the center hole. Each knife pin extends through a corresponding knife opening and is mounted to the rotary cutting disk at a corresponding knife mount location. Each knife pin has a distal keeper with a double keyhole shape which generally approximates and is slightly smaller than the double keyhole shaped opening in each knife. A spring plate is positioned under the cutting disk adjacent to each distal keeper of each knife pin.