Hard to tell from the one angle but top part looks like a bearing housing half. I would guess it was just a bearing mount for a line shaft or something like that.
The half rounded end does mean that it mounted on a shaft of some type. Just some ideas, packer on a haypress, cutting head on a sycle mower, some other heavy oscillating piece?
Maybe a coupling rod from a steam engine to convert back and forth piston motion into rotary motion (or vice-versa). Small for a locomotive but perhaps for a pump or sawmill?