Designed to provide a lens cap in the neutral position, then with the flick of a small lever, also giving you a pinhole and two options for a bokeh filter (in a star and crescent shape).
Simple enough to assemble, could be 3D printed and the internal shut off could quickly be adapted to the shapes you want and new variants printed and assembled back in.
Four screws (maybe a little overkill), but they're the same as found in the main housing. Positioning is done by rotating the side lever and it should lock into place with the internal mechanism thing-a-me-bob.
Tools: Fusion 360 + KeyShot