These new beams for the STEMFIE construction set toy have an open box section; which, for instance, can be used to create a flexible, yielding structure.
You can download them here from this link.
New STEMFIE box-section beams ready for download
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!