Here is a normal 2x4 System X plate, and a 2x4 and 4x4 System X plate (can connect to a 4x6 big plate) and a 2x2 System X plate with round corner for for Playmobil or other dollhouses that are based on Playmobil. This can then be used to build a huge area, for example for the large villa (Family Hauser on Youtube).

The yellow and red pins (Playmobil) sometimes go in tightly.

I'm still a beginner in 3D modeling and 3D printing.