Zinc anode for reducing corrosion in the cooling system. This brass fitting has 1/4" NPT threads with a zinc anode attached. Simply install the threaded fitting anywhere in the radiator or engine cooling system. Keeps engine coolant electrolysis corrosion from attacking engine components.
*We have had success installing this fitting into the threaded port (often unused) on the thermostat housing (see pic). Although the threads are not idenctical (BSPT Vs NPT) they are very similar and with thread sealant it will seal up. The anode will need to be cut off to avoid hitting the thermostat.