This is a 2 - slot Gpu support designed to work with the ATX Motherboard open case (https://makerworld.com/en/models/232528-atx-open-pc-frame?from=search#profileId-266994)

It supports the GPU from lateral movement and prevents it from falling out during transportation. 

I recommend printing the original ATX Case model with a section of 100% infill in the top of the top bar to drill holes and install threaded inserts to hold this suppoty bracket. 

Also to print this model at 100% infill so a hole can be drilled and insert installed in the exact position to mach your GPU configuration.