Measuring For French Doors:

Take the outside measurements of the glass area, including any moulding around the glass. Also note how much flat space is between the moulding and the door knob area. This is important in determining if a 4 sided frame is possible. An alternative is a 3 sides frame where there is no frame on the hardware side. This is useful if the door knob is too close to the glass. If the frame can be installed directly on the moulding by angling the screws, order a 4 sided frame. 

French Door Shutters are installed using the L Frame.

“Outside mount” refers to the L Frame being mounted outside the glass on the face of the interior side of the door, not on the exterior side of the door.