I just scaled one up from the directions here.
http://www.spadtothebone.org/PDF/Buhor.pdf it looks like just over one inch, not 1 3/8". I just used some spacers that were separating 2x4"s at the lumberyard. They were free, I had to sort through for straight and unbroken ones, and ones that were tapered etc. I actually made the wing thicker for an Extra wing. It was 2mm coro though, and it bends nicer. Some of the .15 size wings are run through a table saw to make them thinner, like 7/8ths"