These bungs are great for turning bottles and vases into lights. The slot at the top of the thread is where you can use a screwdriver to tighten the bung, expanding it to fill the void in which it is placed. The wire can run right through them, or if a side entry is used - out at one side. It is well to remember that there are no standard sizes for these, so always measure the opening of the piece you are working on before selecting the bung for it.