This is how the HIH is constructed (from frybrid.com)

First, it is necessary to drill the compression to NPT fittings so that the copper pipe can slide through it. Be careful not to damage the compression side of the connector or it will leak.

This is the same basic idea as the diagram, except using real fittings.

Complete Hose in Hose.

After the hose in hose was complete I noticed that the thickness of the hose barb fitting was causing an unfortunate restriction. This might not have been an issue with larger diameter hose (I'm using 3/4" in this application) but I wanted to have as much coolant flow as possible.

So, a 8" long 1/2" thread NPT pipe was obtained. Without barbs, the pipe was much thinner and would allow for maximum performance but perhaps allow the hose to slip off..

.. which is where the file comes in! The hose was "roughened up" with a file which should allow extreme hose pipe grippage

The hose in hose being installed. It sure helps to have a helper at this point.

Routing the hose in hose under the car.

For more check out: Detailed pictures of hose in hose routing

The Hero