This is a hot shoe mounted rail for a Orion "EZ-FinderII" or Celestron "Star Pointer" red dot astronomy sight. This will allow the use of the EZ-finder to align a telephoto lens to your imaging target.
I'm not sure if there is a name for this rail profile, it's about 15mm wide. This is adapted from from my Picatinny hot-shoe design. It mounts the Celeston red-dot finder (Amazon ASIN B00009X3UU) without need of the foot & rail that would normally attach between the scope and the finder.
It is optimized for the Panasonic G series hotshoes that allow a latching tab, but will fit any standard hotshoe if that is clipped off.
I did not bother to remove the holes for the Picatinny bolt clamp or hex key storage from the remix, but they won't cause any issues.
Print vertical. Add raft if better adhesion is needed.