sub-small shank mouthpiece

[Donn]

Pretty ragged condition even for $25, but if you happen to have the extra small shank receiver that it would fit -

https://www.ebay.com/itm/MUSICAL-INSTRUMENT-MOUTHPIECE-SOLID-BRASS-11-4mm-VINTAGE-TUBA-TROMBONE/223192052704/

Seller says it's 11.4 mm, which would be about 1mm less than bass trombone shank, and at least 1mm more than trombone small shank. It's listed as "baritone", which is probably a good guess - there have been baritone receivers in some intermediate size?