During my time in high school band, drum and bugle corps, and in the military, I encountered 2 sizes of mouthpiece shanks, the usual large and small. Most of my marching horns took a small shank that would fit in a trombone, and my euphoniums used a large shank mouthpiece. I recently acquired an old Besson New Standard (1972). I ordered the SM4M european shank size euphonium mouthpiece, and the end just barely squeezes in the receiver. Is this size of mouthpiece in between the large and small that I am used to? I did some more searching and found that there is a baritone model also, is this the size that I would need? I couldnt find any comparison of external dimensions of the 3 models. Thanks very much for your feedback!