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I think the 32 is roughly the size of a 186, and the 30 is not just a 4 valve 32 but slightly smaller overall. A guy I play with used to play one (a 30) and it was noticeably smaller than the 187 I was on.

It's a 4/4 -- it's got a 17" bell and like a 0.768" bore. I owned a MW-30 stencil a few years back. Very good all-around tuba!