It is a mechanism similar to shutter mechanism. There are two leaves. The shape is similar to Chinese Taiji or Tai Chi. When you rotate the "Drive Part"or the middle plate, the blades inside the center hole can open or close gradually. The center hole's MAX diameter is 30mm, outer size is diameter 74mm and thickness is 8 mm. Most parts are designed for laser cut. The parts' thickness is 2 mm. Most parts can be 3D printed too, it you plan to do that, resin material should be the best option.
Read this tutorial to assemble the mechanism.
Files: https://twothreed.com
Cgtrader: https://www.cgtrader.com/monk3947