This is a very rare vintage Berg Deluxe stainless steel slant signature mouthpiece for tenor. Facing 90/1 with offset M and P stamp on the front of the shank. The stainless steel body is in decent shape with a typical amount of cosmetic wear. The original bite plate is unfortunately missing.
Previously saxophon.org has only seen one other Deluxe mouthpiece in gold brass with a facing of 120/2.