These economical mouthpiece adapters will quickly allow players to play an instrument with a mouthpiece that does not fit into it's receiver. They are great for doublers that may not want to learn a new mouthpiece for marching band or have not yet found their mouthpiece of choice for their new instrument.
Some Rough measurements:
Tenor-Besson large side inner diameter is 12.19mm
small side inner diameter is 10.59mm
small side outer diameter 12.32mm
large side outer diameter up against the collar is 13.95mm
Tenor-Bass large side inner diameter 12.36mm
small side inner diameter 10.67mm
small side outer 12.52mm
large outer 14.2mm