If you have a Magic Trackpad to go with your Magic Keyboard and you hang them on the wall for some reason like RostaP apparently does, then this is the holder for you!
The keyboard side holder is the perfect size for the Magic Keyboard, but it's too shallow for the Magic Trackpad - if you try to use it the trackpad just won't quite slide into place. This takes that holder and basically increases its depth juuuuust enough to fit the trackpad snug into place.
It's designed just like the keyboard side holder, in fact, it's literally just the keyboard side holder but with the holder depth increased slightly. In order to use it, you'll need to print some inserts for your wall, as well as the keyboard bottom holder, which works fine for the trackpad.
Print settings can be whatever you use for your wall, for me:
These don't hold a ton of weight, just make sure they won't break apart when you pull them out.
As a side note, I later discovered the parametric pegs by Chandler Lofland which would theoretically also work. However, I had some difficulty with it (and had already made this model), so I might fork it in the future to improve it. That's a task for future me.