What you are seeing is the rib stithing. It is from Scale Rib Stitch, do a google search.
It is a self adhesive strip with the stitches on top. There is a paper layer over the stitching that you peel off after apply the stitching to the plane. You buy the scale you need then cut them to width. The rib tapes are over top of that and ironed down. I did not apply any dope over the tapes just a coat of primer before paint.

I bought rib tapes and perimeter tapes from Gary for my Waco. I also applied tapes over all the fuse stringers just like the full scale. Adds a nice little touch.
Later!!
Anthony