Do you mean the drain pipe coming down vertically from your sink? Or the drain pipe coming horizontally out of the wall? It would be very rare to have 1 1/4" drain pipe in your wall, especially galvanized (copper maybe, but very unlikely to be 1 1/4" galvanized). So I'm assuming you mean the drain tailpiece coming down from the bottom of your sink. That is normally 1 1/4", and presumably it is chrome if you are saying it is metal (it is also plastic sometimes; generally black or grey). The threads on the bottom of those tail pieces is to screw on a metal drain piece extension if needed. Otherwise, regardless of whether the bottom of your 1 1/4" metal drain tailpiece is metal or plastic, threaded or not, they all go into a pvc p-trap assembly just the same and just as easily. You may be using either a 1 1/4" or 1 1/2" pvc p-trap set; either way, there should be a slip nut on the trap (specifically, the "u" part of the p-trap) that will accept the 1 1/4" drain tailpiece from your sink.
