The ring around the facing edge in the first photo has been machined with what looks like a sealing surface. I think it could have been the flapper from an old check valve. the broken part in the back would be where it fastened to the swing linkage.
Its a brass Pan Weight (sometimes referred to as a trade weight), the lead in fill on the base allowed it to be checked & changed to the official weight. As you can't see all of the verification marks, dating will be difficult, but I would say its 19th C.