Construx 4 Post Hinge Knot

After I had kids, I dug out my old Construx building set, which was my go-to building toy (after Lego) as a kid. Everything was in great shape, but the black knots (connectors) that acted as hinges had become brittle over time and break with the smallest twist. I decided to create a version of them for 3D printing. They may not be any less brittle, but at least I can make new ones as needed.

This version is compatible with the original, meaning that if you broke the center part, this center w