When I was kid, my uncle would often use this word when he was trying to fix something. I suspect he didn't know what to call the thing he was connecting to something else. So he'd use segunafranz as a substitute. And he'd often use the related word "fisteris" with it. He'd say something like: "Well, to fix this it looks like I have to connect this segunafranz here to that fisteris." And as a child, I was impressed with his knowledge of such things that were beyond me. As I grew up, he revealed the truth of the matter: that he didn't have a clue about what he was doing.
pronounced say-GooN-a-frans- Colloquial, used by adults to describe to children an object too complicated to explain. Often used by an adult to cover up the adult's lack of knowledge of the proper term to denote something for which an actual name is not known. Related to "thingamabob." Often used in connection with "fisteris." Example: "You see, we need to connect the segunafranz to this fisteris to make this thing work."