Warburton sax neck set, fits Keilwerth tenor saxophones, content: copper neck, tenon for Keilwerth instruments, 3 initiators (mouthpiece receivers) F50, A50, S50 with different backbores, A50 (1/3 cylindrical): bright and centered sound, perfect for jazz and contemporary playing styles, F50 (2/3 cylindrical): the lower register is big and warm with an excellent subtone and the upper register is fluid and singing, perfect for jazz, S50 (straight cylinder): most balanced in terms of lows, mids, and highs in the sound, perfect for contemporary styles