I designed and tested these a while ago. 

There is a GTX version, tested with GTX 900 an GTX 1000 series GPUs. But should also fit GTX 700 series.

And an RTX version that has been tested to fit with RTX 2000 series GPUs.

RTX 3000, RTX 4000, and RTX 5000 GPUs all changed the mount points that these use, so they are not compatible.

These use the support bracket attachment at the end of the GPU, and have only been tested with the NVIDIA manufactured Founders Edition GPUs. They may still work with other brands GPUs, but your mileage may vary.

You will also need 2x M3 screws of a minimum 4mm length, absolute maximum of 10mm length. Somewhere around 5-6mm seems ideal. Exceeding that length can lead to damaging your GPU.