For one product, I'd like a part to be held within a larger frame, and to let the inner part rotate by (probably) 20 degrees or so. It will not be a separate free-moving part, but joined to the frame, with limited mobility. I'd like to join it by a strip or wire of material, so the whole thing is one piece. What should I know about designing this strip or wire? How flexible is each of the materials I could use? How flexible is a long thin part? Are there graphs or empirical formula to estimate spring constant from geometry? The image shows, crudely, some types of springs I'm considering. The inner disk will rotate about the red axis (by means not shown) but only a few degrees.