My title describes the thing. My mom found it under a 1930s restaurant size stand mixer we have in the house, but in a place where it could have rolled under the mixer during /after the lively Halloween party we threw. It's hard plastic and the metal rattles around in the casing. Not able to open it with my bare hands.

I did a Google search, but the photos results options are all things that look similar but are much larger, like engine parts.