This is an outstanding vintage M.C. Gregory Model A Tenor mouthpiece serial number 3790. It is an original 4A with the large 20 chamber. The piece measures out right at .083". The piece is extremely free blowing and takes the air incredibly well. These vintage Model A mouthpieces are known for the way they vibrate, and this is a great example of craftsmanship that Gregory put into his mouthpieces.