Okay, if you are trying to "export" a small design you make in the ship designer to then import into a different design, I believe that this feature is no longer supported. A while back, in the early going of the ship designer, you could export I think. But as of now, I don't believe you can do it. (I may be wrong).
One option, depending on the scale of what you want imported, is to save your part as a template. And then start with it when building a new ship, but offset it from center and build your new main structure, keeping the templated part to the side and then moving it in place once you know where it goes.
