The Magic Square Cash is named for its resemblance to a Chinese coin with a hole in the center. Here, it is folded from mono-color triangles. See PDF diagrams.
The sliding action on this modular design can transform a square-holed octagon,
which resembles an ancient Chinese coin (cash), to a square, and vice versa.
The common 6-inch (15 cm) commercial kami is a bit flimsy for this design.
Use 3-inch or smaller commercial kami to make a smaller model or use thicker
20-lb. (75 gsm) or heavier paper to make a larger model.
Editor’s Note: Heavier paper works well, even for a small model.
The Magic Coin Star II. The Magic Square Cash is based on this earlier model by Sy Chen. Try reverse engineering the star from the square-based version of the Magic Square Cash on page 3 of the diagrams. (Hints: The model looks the same on both sides. All pockets are hidden inside. One additional fold is required.)