Bob Reeves Trumpet Mouthpiece Underparts contain the cup, bore, and shank. Each is designed to create a different sound, and is optimized for a different playing style.
692sL Backbore - Shorter than a conventional mouthpiece that is very efficient for playing in the upper register. When added to a deep cup the tone becomes dark, but still retains easy access to the upper register.
B cup - Deep cylindrical bowl similar to a Bach 7B