Constance - I have a Getzen Eterna cornet that I play in a brass band (very nice playing horn) and the 7C mouth piece that came with the horn has a slightly larger dia. and is definitely deeper then my Bach 7C. Rowuk is right, no one can tell which m.p. you should use via Internet. Forget what people in the past told you, you need to find a m.p. that works for you period. Work on your basics, lip slurs and long tones and get a good teacher. Good luck and have fun.