This TUBA / Sousaphone mouthpiece is actually classified as a "doubler". Yes, it has the famous AL Cass Trombone rim which is for the trombonist who wants to play TUBA or Sousaphone! I have seen just 2 finished examples of this model in 10 years on ebay.
This very well could be the finest example in existence!!!!!!!!! If not among the top 2.