For a very long time Besson (or Boosey & Hawkes) made the "gold standard" for euphoniums. Until 1974, Besson used a medium-sized receiver for the mouthpiece. This is midway in size between the small (tenor-trombone-size) mouthpiece shank and the large (bass-trombone-size) shank. It is sometimes called the "European euphonium" shank. As far as I know, trombones never used that size. Today, most makers of gold-standard euphoniums, and many makers of student-level euphoniums, use a bass-trombone-size receiver. At least one euphonium maker (Willson) has a model that requires the European euphonium shank.

Because this medium shank is relatively rare, it is difficult to find a mouthpiece that fits. I have compiled a list of mouthpieces available in the medium shank, and it is not a very large list. The list of large shank mouthpieces is 4-5 times as long.

One option that may work for a medium-shank euphonium is to use a large-shank mouthpiece and have a repair shop use a lathe to narrow the shank enough to fit. I had that done when I was in college. I need a Bach 5GB on my Besson euphonium, but it was not available (and still is not). I purchased a large shank model and took it to the shop's back room, where in a few minutes they had fitted it to my horn. The shop did not narrow the entire shank, but only went far enough so that it would fit the receiver. Attached is a photo of the mouthpiece (sorry about the tarnish - it doesn't get out much these days!). All that is required is that the mouthpiece have a thick-enough shank wall so that the material can be removed safely.

This would allow you to have an enormous selection of mouthpieces to fit a Willson or older Besson. Another option is to forum member Doug Elliott produce a custom mouthpiece for you. It could have a removable shank so that you could also use it in a bass trombone receiver just by having two shanks.

Some players recommend having a repair shop replace the euphonium's medium receiver with a large receiver. Others say this is not good because it changes the nature of the instrument. I will not wade into that particular argument!
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