I had several folks interested in the brass threads that were used in the cherry urn I posted, so I picked up another of the plumbing parts today so I could post pics. This piece is apparently called a "knuckle joint." The opening is about 2".
The nut was used for the female thread insert in the bottom of the urn by turning away the lugs and truing up the whole piece. It was flipped over and the face was turned to remove most of the rough texture. Then a portion of the male threaded piece was parted off to use on the lid/plug.
Hope this helps!