This is not my original wor and the cover is not mine either the original was on Thingiverse and the link is below.

https://www.***********.com/thing:4841850 Please link to my video and article if you use this, thanks!https://www.youtube.com/watch?v=DAngcygU7tc&ab_channel=JelleRommers https://www.sciencedirect.com/science/article/pii/S0141635921000726?via%3Dihub#appsec1

EDIT: the model from the YT video is "Tetra1_Requiring_supports.STL".

No need for flexible material, regular PLA works fine.
The thin walls are 0.7 mm, this worked best on a Prusa printer with a nozzle of 0.4 mm, it then creates two lines with a small overlap.
The rotation point of the Tetra 1 design is located 115 mm from the top of the joint
The rotation point of the Tetra 2 design is at 50 mm distance from the surface of the joint
I have added some templates to create your custom joint

Also check out the upload from juani_cer https://www.***********.com/thing:4808398he replicated the Tetra II design from my article and Johnrandersen added a pen to it.

Edit: ThinkingPegasus created a remix of this particular design as well!

Thanks everyone for your contribution, great to see how much the design is used. Juani_cer also made a joystick out of it: https://www.youtube.com/watch?v=n7yjRrHE-SI&ab_channel=jicerr

Plus, someone put a chicken head on it?! https://www.youtube.com/watch?v=taodni2Mc7Q&ab_channel=50%ED%94%84%EB%A1%9C

Spherical flexure joint 1and 2

0.2mm layer, 2 walls, 15% infill

0.2mm layer, 2 walls, 15% infill

0.2mm layer, 2 walls, 15% infill