Manipulative snap-together sprues to create polygons, polyhedra, molecules etc
Meant originally to teach the relationships between angle measures and side lengths in triangles and polygons in general. The power here is that you can make polygons with unusual angles and side lengths -- thus requiring students to measure. If used correctly, many protractors will lay right across the top for easy measurement.
Because I couldn't find any connecting objects with length options which were relatively prime, I decided to make some. Here we have evenly spaced rings and vertical pins, but horizontal pins are arranged in a slightly different pattern allowing you to make regular or irregular polygons.
These are for teaching plane geometry only; I haven't decided whether a 3D geometry version is warranted. I have seen how amazed students are when they roll off the printer and students can suddenly build things!
I usually make them at 1.25 magnification.