Hi! I’m a Euphonium player from Sweden and this is my first post on this splendid forum. I'm having some trouble with (what looks like) cold sores on my lips and have therefore bought a plastic Kelly mouthpiece. It’s size 5G and should supposedly fit my Yamaha euphonium, but it didn’t. My Yamaha YEP 321 have a quite small shank and the mouthpiece was to large. Now that I'm taking it back to the store, I'm wonder about the different sizes. Does anyone know which of Kelly’s mouthpieces are suitable for a Yamaha YEP 321? If so, what difference in sound do they produce? I play all kinds of music – marches, jazz, pop songs – and I like to play it loud. I would like to improve my higher playing though, so I guess a shallow mouthpiece would be good. But on the other hand, I like to have a distinct tone and I’ve read that a deep piece allows for better precision. My current Yamaha mouthpiece is size 48. Thanks in advance.