I used this to mount 2 SSDs on one HDD tray. The overall height from the very top of the top drive to the bottom of the bottom drive is 1 inch, which is the thickness of a 3.5 in. HDD. I uploaded Sketchup file, so you can customize the thickness as you wish. The file here is set at 6mm thick, just because I happen to have some 10mm screws laying around, feel free to customize it. Please note the adapter has top/down orientation. Top screw holes are 4mm away from the edge where the bottom holes are 3mm away from the edge. This is done to fit those modern 7mm thickness drives.