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I have in my posession a euphonium mouthpiece marked Willson 51D-3. It seems relatively similar in size to a Wick SM4 in depth, though most noticably has a differing rim contour. Anyone know of where I can find the specs for Willson mouthpieces? Or perhaps whatever company makes them? I've tried googleing a few tries, but to no avail.

they're made by DEG

there's a good tbone mouthpiece comparison chart here where you can find 51D but I don't know what the 3 is.
www.ibowtie.com