the answer to your question is simple. You will need a 3/8in compression fitting with the appropriate thread. First, you cut off the very end of the barbed end on your radiator. Make sure you leave enough tube to install a compression fitting though. Then you put the 3/8in compression fitting on the tube of the radiator and tighten it up. The one I have is a 3/8in compression fitting with a 1/4in npt thread. I then screw a 1/4in npt thread with a 3/8in hose barbed end. This may sound complicated. Here is the article where I did mine. You might be able to get an idea if you looked at it.
http://www.procooling.com/html/how_t...r_to_yer.shtml
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ondaedg@procooling.com