Abstract: An insulating outer shell includes structure forming a first opening in a first end of the outer shell, and structure forming a second opening in a second end of the outer shell. A conductive inner shell having a closed end and an open end is fitted inside the outer shell such that the closed end is oriented toward the first end of the outer shell and the open end is oriented toward the second end of the outer shell. A first conductor extends through the first opening of the outer shell. One end of the first conductor is welded to the closed end of the inner shell. The first conductor has a free end. A spring for engaging at least one second conductor within the inner shell is welded to the inside of the inner shell.