3C = easy blowing mouthpiece with good projection
4C = The Yamaha YAC-1286 4C mouthpiece makes it easy to obtain a balanced, clear and focused tone in any octave. Everyone from professionals to beginners like this mouthpiece.
5C = Popular with soloists.
The Yamaha YAC-12874 5C Alto Sax mouthpiece provides a somewhat richer tone with greater variety of colors than 4C in addition to excellent flexibility and response
6C = Has a more open tip, making this an excellent choice for experienced players looking for powerful volume and a rich sound.