Private Die Proprietary RS40b.  A beautifully centered stamp that would be desirable in any collection. The stamp has a small thin but otherwise is fault free. 

I have many more quality U.S. stamps available for sale that are not yet listed on my site. I have 1st through 3rd issue Revenues, Red's and Green's, Match and Medicine, as well as some Newspapers, Officials, and Telegraphs. Please check in on my site to see new stamps that are being put on weekly. Thank you.