While the values of other attributes can change, the value of the self attribute cannot change. The self represents the part itself, and you cannot change that basic definition of the part. Therefore, if you connect the self attribute of one part to the self attribute of another part, nothing happens. In general, you do not want to connect two self attributes of different parts.

If you add the self attribute to the interface it is the same as if you tore off that attribute and placed it on the free-form surface. When adding an attribute to the interface, the attribute is added to the connect menu for the free-form surface. When tearing off an attribute, such as the self attribute, the attribute is represented visually on the free-form surface for you to interact with.