Anybody know fitting for the transmission lines into the radiator? Bought 3/8 NPT plugs and they're a shave too big. The hose side fit into the 3/8 fittings on the shelf and the threads on the plug matched so i assumed, since it's 3/8 hose, should be 3/8 NPT. Apparently not. So what B.S. metric dimensions do I need? The plugs I bought are hand-tight at like 1/4-1/2 turn.

3/8 = 10mm , 18 TPI = 1.41mm pitch . So like an M10 x 1.5 plug? -> 0.675 OD for the 3/8 fitting is M17 equiv. Nearest would be M16 x 1.5 ?

 

Ooooooops

 

for the record, the correct answer is an inverted flare plug. They come as 2 definitions for the same thing: 5/8-18 thread, or 3/8" flare.