I want to use a rectangular cross section to act as a torsion spring that can be adjusted. The idea is that the adjustment would be made via rotating the rectangular cross section about it's center at an angle theta. I've used parallel axis theorem before, but I don't think that is applicable here since it is just one shape. How can I calculate the polar moment of inertia so that I can then use other stress equations? If you're curious for what it's for, it's intended to be a blade type anti-roll bar. Thanks for the help!