This is a clip for the X-column of the openlock system. With the normal clip you can only attach 2 walls to the X-column, but with this clip you can add 4 walls. I combined 2 normal openlock clips to make this.

On the picture it is visible in the column found on https://www.printablescenery.com/product/column-and-buttress/

I mainly made this because I was frustrated I couldn't attach walls in an X-pattern with the default clips.