I'm brewing up a modular test equipment form factor. I want something that is modular, but isn't one of the form factors made for a full-sized rack (e.g. 19"). Something along the lines of VME64x, CompactPCI, IEEE 1101.10, etc but not as chunky. I want something that is the same size as all of the rest of my benchtop equipment.

I often need to rig up some hardware-in-the-loop and it would be nice to have a single unit that has GPIO, maybe a high accuracy ADC, DAC, etc. All accessible over ethernet and/or USB.

I got these nice power entry modules from Schaffner. They give you a nice IEC connector, a switch, a fuse, and good filtering (choke, X and Y caps, etc).

I'd want to leverage as much COTS components as I can, so I am thinking to use existing card specifications, but give it a haircut.

I measured all of the various kit on my bench and shelves and came up with an average chassis size (usually it's the depth that varies anyway). I sawed these rails down to size making sure their card alignments were in the right spots. I think this would be a good size.