This function demonstrates the STEMFIE bidirectional spring-pin connection. It uses an expanding flexible section to lock the pin inside a beam. The protruding ends are used as locating pins onto which a U-shaped brace assembly can rotate.
The free and never-ending 3D-printable educational construction-set toy you can download and make at home!
This toy is unsuitable for children under three years due to choking hazards! 
