Long time lurker here. I have a cluster of Lenovo Thinkcenter Tiny nodes (M900/M910Q/M80Q) that I’ve been playing around with MAAS and kubernetes with. I’ve been looking at with getting Mellanox network cards to work with an M.2 to PCIe adapter (turns out you can get ~20Gb through it!) and decided that over time I’ve going to upgrade my entire cluster with maxed out networking.
I was afraid of the cards shorting out against the other metal in the rack, so I designed a 3d Printed cage for these machines. The cool thing about it is that underneath the bottom backplate of M910Q and M80Q machines there are motherboard screwholes that go all the way through, so you can use regular motherboard screws to fix a cage like this to the underside 
The M900 machines don’t have a removable underside so I’ll figure something else out.
Super pleased with how this came out.
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I’ve put the entire FreeCAD project and stls on thingiverse if you want to use or modify this design.