This is a basic version of the SGI Octane hdd drive sled/caddy. It does not have the locking mechanism or the electromagnetic shielding, but works better than the common "pair of floppies." The front looks similar to the original, but is not exact. The rails are exact. They are meant to be used with rubber vibration mounts.
Carefully measuring an original sled for the screw positions relative to the rail positions, leaving lots of space in the front for air ventalation and optional EM shielding.