This is an Arwin 9B trombone mouthpiece, Don Reinhardt model. Stamped on the mouthpiece cup on one side is "Arwin", on the opposite side is stamped " DON REINHARDT MODEL". On the lower side of the bowl is stamped "9B". This mouthpiece came from the estate of a dear friend who told me before he passed that he had been a student of Dr. Reinhardt, and had the utmost respect for his teachings. I know nothing else about the history of the piece. It is in very good, although not perfect, shape. The inside cup diameter at the rim is 25.0mm, and the venturi just clears a 17/64" bit. There surely cannot be many of these around. For more information on Dr. Donald S. Reinhardt, please check out the website, findable by searching for 'Reinhardt Foundation'.