Breslmair 3-piece type Backbore Backbore Number: P Throat Diameter: 3.80 mm Description: A common model for orchestras, with a soaring resonance. Short shank (formerly: Bach-Yamaha shank) The shank (outer part) of this backbore is made to be approximately the same thickness as Bach and Yamaha. Recommended for instruments from old East German manufacturers and piston trumpets. ※ In some piston trumpets, the tip of this shank may hit the back of the mouthpiece receiver, making it feel like it's touching the mouthpipe. This phenomenon occurs because the taper varies slightly depending on the receiver. The actual distance between the mouthpipe and the tip of the mouthpiece is the ideal distance (2-3mm). If it feels a little loose, it will stabilize if you insert the mouthpiece while gently twisting it.