Posted this to reddit some time back, reposting here because I want to contribute some content and help lemmy gain popularity.
I hope that in a few weeks I will be posting an updated version of the setup with the laptop replaced by a third monitor and a few other modifications.
It’s pretty much just a metal plate with some holes, I wouldn’t worry to much about it.
For me, it was surprisingly hard to find one with the correct dimensions and color (white). After quite a lot of searching I just bought the only one I found matching the criteria. It was called “PureMounts PM-ADAPT-A” on Amazon. It attaches to the monitor arm through a VESA mount.