This is a simple mount for Brennenstuhl Premium-Alu-Line Extension Sockets. It's designed for 4 mm screws and tight-fit.
Use two of them per extension socket. Position them using the aluminium profile, slide it in and finally reassemble the extension socket.
I printed them laying on the side with five contour lines. They are quite rigid, so less contour lines might work better for you.
The author hasn't provided the model origin yet.