This is a B shank, which is not often found on the market. The shank is designed to fit small shank flugelhorns, such as those made by Bach and Courtois. The inner diameter is 16.70mm according to the official website. It has a deep V cup and feels slightly longer overall. I felt it was easy to handle, suitable for classical, jazz, and even wind band music. Regarding the "special" designation, there is no mention of this model number online, but it is likely made with the aim of achieving the "ideal 6 size," similar to other special specifications.