Is this an accoustic violin? First there is a "knob" (endpin) on the side of the violin, then there is a "string" (tailgut) with two swrews that are attached to the thing tailpiece the real strings are attached to.
Can't really get what is metal here on an ordinary violin. But it might be the whole tail-piece that is missing. Ask in a music store, it is easy to fix it, but you must be very careful not tomove the soundpost inside the violin. Good luck
Della Daul, June 2006