I put my GPU into that long slot on my motherboard meant for it but I don't know how to screw the GPU because I don't see anything screwable except maybe some holes on the left but I know it must be screwed or something so that it lies 180 degrees (perfectly horizontal) and currently it slightly slants and on the external side you can see its plug holes don't line up parallel to the case so it's for sure. My case is DeepCool Tesseract SW and GPU is GTX 1050 Ti. Here's reference picture: https://ibb.co/nyxHXb