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Math Puzzle, String, Bead, Topology

3D model description

This is one of my favorite mechanical puzzles in the category of recreational topology. It is easy to make using wooden materials. For the curious minds, here is a 3D version. Once the two parts-- the board/stick and the bead-- are printed. Please use a piece of string (rope, yarn) to assemble it as illustrated. The challenge is to move the bead from the left to the right or vice versa. The main idea is to move the knot back and forth through the middle opening. Let's me not spoil the fun of the puzzle here.


Gardner, Martin, 2008. Origami, Eleusis, and the Soma Cube. Cambridge University Press.

3D printing settings




Doesn't Matter





(1) The board does not require a raft or support. The bead needs some raft for adhesion.

(2) The board is about 15mm thick by default. Feel free to scale it to any thickness you like. It won''t affect the puzzle.

Assemble as illustrated. You need a string that is about 8 inches or longer. Make a BIG knot of or glue the end of the string so they will not come out when being pulled. Plastic strings are actually easier to use.

  • 3D model format: STL


STEAM educator, learning from and working with K-12 STEAM teachers to explore new ideas of teaching and engagement. I firmly believe ART is at the core of STEM learning or all human learning! I owe my ideas and designs to the hundreds of K-12 children and teachers and university professors I have had the pleasure of working with, in multiple disciplines-- math, science,engineering language arts, social studies, early childhood education and more! All mistakes, of course, are mine! There is no warranty or liability whatsoever implied or explicit behind the designs or ideas. They are all posted for their potential educational values.

When working with children, please strictly observe all safety and health procedures! Please refer to the NSTA safety guides:




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