Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4625637.
This is my motherboard I/O shield and PCI backplate, designed to fit in a wooden box for my PC in a desk project. My version assumes 9 or 10mm plywood walls.
I have added a version for anyone who wants to attach it internally. This second version has a 1mm clearance with screwholes instead of a 10mm push-through length.
Although I'm uploading it before I've printed this particular version myself, the prototype's dimensions were perfect except for the thickness of the walls between the PCI slots that may have prevented some plugs from reaching their ports. This fits exactly with my motherboard mounting plate and is designed strictly around ATX specifications with regards to distance from chassis floor etc. so in theory it it is compatible with any other.