This is a custom made keyboard case specifically for the Polarity Works BT75. It has a slightly slanted profile and a “slot” for the originl battery. Due to its simple nature it should be compatible with many other 75% keyboards - the deciding factor is likely to be the usb-c port placement. I printed this case in two pieces (cut set in the slicer) and it works for me. The standoffs can be drilled into to make a thread for the screws. Any appropriately sized screw should work.
The author marked this model as their own original creation.