I found this mouthpiece in the case of an old trombone bought from ebay.

Stamped H.N. White Co.28 Equa-tru.

Probably from the 1930's ?

Inner rim diameter = 0.980" Bore = 0.238"

Cup depth same as a Bach 9, but different shape.

A good player in my .500 horns.

Probably considered a "big" mouthpiece in its day ?

Is anybody here familiar with this mouthpiece ?