Zero-Leak Gold® Standard Thread Port Plugs Zero-Leak Gold® port plugs provide an afforadable, realistic method to obtain a zero leak performance. They utlize the following dual method to ensure a complete, zero leak seal: The tapered plug makes contact with the port taper for a metal-to-metal seal; A small diameter O-ring fits between the plug taper and the thread and acts as a back-up seal. The socket-head design allows the port plug to be utlized and removed with ease. The plug is made from ductile iron with a zinc chromate plating. This plating prevents oxidation and corrosion to the plug and ensures a long time use in a wide variety of environments.