Adjustable automatic flex arm lockout

A cutter bar lockout mechanism for a header of an agricultural vehicle, said cutter bar lockout mechanism comprising:

• a shaft having a first end that is coupled to a frame of the header, and a second end that is positioned either on, within or adjacent a cutter bar support arm (arm) of the header;
• an upper stop that is either mounted to the shaft or forms part of the shaft and is configured to selectively interact with an upper surface of the arm;
• a lower stop that is either mounted to the shaft or forms part of the shaft and is configured to selectively interact with a lower surface of the arm;
• wherein the shaft is movable relative to both the frame and the arm between an unlocked position and a locked position, wherein in the unlocked position of the shaft, the upper stop and the lower stop are positioned at a location along the arm where a vertical gap exists between the arm and one or both of the upper stop and the lower stop so as to enable rotation of the arm relative to the frame, and, wherein in the locked position of the shaft, the upper stop and the lower stop are positioned at a location along the arm where the arm is sandwiched between the upper stop and the lower stop so as to either limit or prevent rotation of the arm relative to the frame.