Found at Reuse Center.  Nut is stamped: DICK.  From what I've read on the interwebs, Dick Brothers was a brass goods foundry in the early 20th century, located in Reading, PA.  I believe this part is for connecting a wall-mounted faucet to 1/2" nipples that would extend through the wall.  Please study the photos to be sure it is the right part for your application.
Thanks for looking.