They sound similar, but are different prices. We explain the differences and which will be most appropriate for you...
The Yamaha 4C mouthpiece belongs to Yamaha's Standard Series, which is a range designed for students. This mouthpiece (which is available for the full range of clarinets and saxophones) is made of high quality phenol resin (plastic).
These mouthpieces have been the best-selling for years, because they are are extremely consistent and offer excellent value. Along with the material, the 4C is different to the 4CM in its design; the facing of the mouthpiece is slightly shorter than the Custom Series, which makes them easier to blow- exactly what you need when starting out.
The Custom Series of mouthpieces are designed for advancing students. These mouthpiece are made from ebonite, which has different properties to plastic. This denser material gives a richer tone and allows for more flexibility in tonal colour.