These are cases for bone conductor transducers with mounting attachments for glasses. The housing encapsulates the transducer and has a slot for wires to connect to your amplifier. A full build is detailed on my site, in the post linked here.
Part 1 is the cover and works on both sides of the head.
Part 2 and Part 3 are the left and right sided versions of the glasses mount.
Please feel free to make and remix this design. I really like to see what people have done, so please post pictures if you make something like this or related to it.