Electric Fan Set Up... Help!!!

[elks]

So ai going to set up an electric fan for my truck. I have the following kit in my garage bought from a local yard sale...

http://www.summitracing.com/parts/sum-890015

3/8-18 NPT threaded thermostat. I beleive that this is too small to be placed into the a plug hole on the heads? What size do I need? Is there an adapter or do i need a new unit?

My truck is up at the "shop" which I will not be able to get into until the 15th. I want to have parts ready when I can get to it...