These are tunnel tiles. - you can put other tiles on them.
They come in two angles: 120 degrees and 180 degrees.
Initially I designed for my zigzag models. I'm sure you'll want to use them for the bottom layer of zigzag.
https://www.printables.com/model/1032016-zigzag-fall-for-gravitrax-v2-vertical-version
https://www.printables.com/model/1032051-zigzag-fall-for-gravitrax-v2-spiral-version
I didn't want to lose sight of the ball inside the tunnel, so I made an oval window to see it move.
If you plan to use them higher up in the zigzag, I recommend using the round-bottomed version for a cleaner look.
The author marked this model as their own original creation.