64
Metal, about 1 inch in diameter
(i.imgur.com)
Let us help you identify that mysterious object you’ve found.
Currently in CHALLENGE mode: If you've got something obscure knocking about, post a picture, and let's see how we do. Please prefix such posts with "CHALLENGE:" so we know we've got a fighting chance.
The lid screws in.
There are three holes equidistant around the perimeter. They do not go all the way through.
Really? Then my guess is those may be for a tool to hook into for turning. All in all it looks like something pressure line or liquid line related