Coolant temp sensor as recommended by VDO to work with the OEM gauges.(Part #323-057). 1/8 - 27 NPT to 300'F. As seen in the previous pics, an adapter can be made from the 12 valves' 3/4" NPT OEM sender with some simple machining. I did it with a drill press, a 1/8"-27 NPT tap and a couple of drill bits. Haven't got the rad in yet so will comment if it actually works when I finally get to run it up to temp.