A mount designed for the specific TL-smoother model I got. Since these boards aren't standardized, you may need to tweak the model to fit the board you got. (FreeCAD model included)
The board should friction-fit in, but for good measure has lips on the bottom.
Insert at a slight angle, then push the board in.
Best to print this upright (no supports, maybe a brim to help stand), and using PETG. Or rather, avoid PLA because the TL-smoothers run fairly hot and it might not hold shape over time.
The author hasn't provided the model origin yet.