Diameter of shank needed for Imperial/New Standard

[AndyCat]

Hi all, trying to turn down a mouthpiece for a friend quickly, he has a besson Imperial BBb with the smaller receiver. What diameter does need to be?

[iiipopes]

.490 inches at the outside diameter tip of shank. (12.45 mm)

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[Doug Elliott]

.490 end with a taper of .050" per inch should work.

Most standard mouthpieces will end up with the end too thin and/or the backbore too big after turning down the outside that much.

[PaulTkachenko]

I could do with a standard receiver for my 621 Bb, which for some reason is a smaller than it should be. It should fit too, right?