That's an old "plug in a plug" usually installed by the quick lube places when dealing with a stripped out pan. There is a gasket on the big part that self taps into the pan and has a gasket (and stays there). The small part has a pipe thread.........Put some teflon tape on the small plug when you change your oil, and make sure that you use a larger wrench on the big lug when you loosen and tighten the smaller plug........Or fix it properly :)
