This is part of the linkage from a mechanical bathroom scale. Its made out of cast iron and I don't have the missing piece. The scale has a max capacity of 120kg and the missing piece is one of four posts that carry the weight when you are standing on it.

My idea is to drill and tap a hole (6mm?), loctite a bolt into it and shape the the part that sticks out into the triangle. something like Pic. 4