Funny - I am currently devloping such an item for my AT-ST driver costume.
The AT-ST helmets use a similar device and are not covered.
What you see is a box with rounded edges approx. 4cm length and 4,5cm height as a base. I guess the depth is around the 1,5 cm mark at the top, maybe 2.
On the box there is 1 bigger round button in the upper left corner and two smaller ones in the lower right.
The main piece is what I believe has to be the rear half of the carbouretor part of the Revell/Renwal 8V engine kit that was used in several sw parts. (It is definately not the front half except the intake like part)
- thanks to marcus o. here from the boards for the V8 hint -
Above the carbouretor part there is half a dish and conic cylinder ending at the border of the box.
On top of the box there is another cone shape with something rectangular holding the cut "ring".
Here are a few screen caps: (I might release my technical drawings once I finished mine)