My home NAS server is about 6 years old and has 4 hot-swap SSD bays which are used for the data volumes. The OS was installed on a Compact Flash card, which despite giving excellent service, got fritzed when I turned it off to clean the office (moral: never turn things off if they're working and covered in dust!) The CF card was in an adapter which was mounted on the white pegs you can see in the photos.
The quickest and cheapest option to get the server up and running again was to replace the CF with an SSD. Having nothing proprietary to mount the SSD onto though meant I was able to bring 3D printing to the rescue with the attached Blender and STL model. Quite a long print, but light, perfectly-sized and all the holes lining up means it does just what I needed (though I'm not actually going to use the ReadyCache disk - that was just to check dimensions).
There's a lip round the back outside edge for a little extra stability though I dont think it's really necessary. The pegs on the back are to provide a stand-off and match the depth of the mounting pegs in my chassis - you could leave them off, or adjust their height to suit.