Electrically Isolated FeedThrough for Lightning Arrestor

I needed an insulated feed through for an antenna lightning arrestor I'm building for shortwave radio. The STLs as presented are specific to my application, but I am including the FreeCAD file as well, in case you need to modify this to fit your own use.

As is, the feedthrough is designed to these specifications:

* Screw size is m4.
* The mounting hole is drilled out to 11/32".
* The material is 2.5mm thick.
* The shoulder is 18.75mm in diameter.

To modify this for your own needs, you only need to change the parameters in *Sketch* under *bushing*. The four constraints you need should be red. There are two construction lines - one for the thickness of the walls and one for the diameter of the screw. The shoulder diameter and the material thickness are modified on the actual drawing.

If you are interested in the lightning arrestor itself, it's just a scrap piece of aluminum angle into which I've drilled and tapped three holes appropriate to the spark plugs