Another Way to Make Pleated-Ribbon Trim
This technique relies on a knife pleat, spaced so the leading edges of the finished pleats are one half a ribbon width apart, and the return of the pleat is half the ribbon width.
For this technique, I use "ribbon width" as the unit of measure, which I learned from Candice Kling's book, The Artful Ribbon (C&T Publishing, 1996). Using the width of the ribbon as the increment of measurement makes this trim easily scalable to any size ribbon.
I am also using paper, as well as the ribbon to demonstrate this technique, as that seems to be a well-received way of demonstrating this kind of thing.
You'll mark the back of the ribbon to pleat it, as shown in the photo here. I explain how in the next step.
The paper model is marked in red for the leading edges of the pleats, and with blue for the back folds for the returns of the pleats.
In marking, you can see that the distance between the leading edges is one and one half ribbon widths apart--this accounts for the return of the pleat, which is a half ribbon width apart. This is the distance between the red lines.
There is one ribbon width between the leading edge and the pleat's return fold to the right, and half a ribbon width between leading edge and the back folds on the left. This produces the blue lines.