While exhibiting at the PRI (Performance Racing Industry)show, we realized there was a need for a tool to mill heads and blocks on a Bridgeport. The only tool available at the time was a "bar" with one or two inserts. The inherent problem with something like that is you get "bounce" as the insert hits material after swinging through air. We came up with the idea to make a more typical face mill with up to 10 inserts so there will always be multiple inserts cutting.

The shell mill is made from 6061-T6 aerospace aluminum for durability, but light enough at the same time to use in a Bridgeport type machine. We also made it so it can be used with a standard 1-1/2" shell mill arbor that is available in R8, CT-40, etc. It take standard APKT inserts that are readily available and come in grades for cutting aluminum, cast iron, steel, stainless steel and the high temp alloys.
We sell a lot of tooling across the gamut of industrial machining, but this is the one tool people call us back about to tell us how much they love it. The face mills come in 10" for big block heads, 8" for small blocks and 6" for motorcycles and outboard motors. 
When milling an aluminum head, you can slow your feed rate and get a mirror like finish; required for high performance motors with metal gaskets!