RV Day / Night Shades are uniquely designed for the rigors and functional needs for use in a moving vehicle. These window coverings are manufactured by many different companies, and because of that, can vary in design and in materials used. They generally incorporate a tension system which allows the shade to be anchored to the wall, and tightened or loosened, based on preference.
Here are some diagrams that illustrate how the internal strings are routed and how they connect to the internal springs:
Here’s a restringing video for the RV Day/Night Shade:
Parts and string for RV Day / Night Shades can be found at FixMyBlinds.com