I am selling this item because I purchased it but have not had the opportunity to use it. The inner rim diameter size is Bach 3-5. The cup is about the middle of Bach E-F. The 19 backbore is a backbore that many professional players have been using recently. It is a little tighter than the standard one, so it has a good sound projection and a feeling of carrying sound. You can play from low to high notes without stress, and the cup is not small, so you won't feel cramped on your lips. The combination of a 43S and a 19 backbore is a mouthpiece that makes it easy to control the sound. This is a 2-piece model. I am a non-smoker and do not own any pets.