This is a typical section from the sides of the 13a horn, one of the 120 needed to make one 13a horn.
The shape is like a propeller, end is rounded to follow horn profile and the two straight edges are not parallel (that would be too easy don’t you think!).
These side sections are finished to 1 inch thickness. To achieve the desired shape a 2″ thick piece is required. They are very difficult to plot and then extremely difficult to clamp securely for hand shaping. The shaping is down to craft and experience and sharp tools….I’ve done 1000’s of these over the years making the 12a and 13a horns and I still smile when I get the “perfect one”….the one shown is pretty spot on…