This is a GR 63MS, which has become a rare item in Japan. Normally made with a #2 backbore, I requested it to be made with the narrowest T-72S backbore. It's about the size of a 7D backbore, but with a comfortable resistance that allows you to reach high notes, even in the lead register. It was a little too big for me, so I'm selling it to someone who needs it. The custom specifications cost extra and take more time, and the current supply is quite unstable, so it's uncertain if it will be available in the future. Official website description--- T-72S Backbore Our tightest commercial backbore. High-compression design for a huge, thick sound core. More free-blowing than our "commercial" backbores, with greater volume! Ideal for large-bore horns. Available with optional earplugs for saxophone players. (Just kidding) Pierces like a laser. Truly like a giant laser.