Thanks for that. Now I see that it is for the mouthpiece. But why rubber sheet ? I would have thought that a hard plastic might be better.
Earlier in the thread someone had mentioned tonehole crescents which made me think it was for that or somehow for the sax bore.
I look forward to hearing how you get on.
I guess rubber can be easier to adapt to different pieces, and I bought some beautiful rubber sheet.
Eventually I will try to work out some neck design too: my endorsee will start experimenting shortly with them. Until now he got them right: I am having fun with my new Sequoia Lemonette soprano, with the beauty of four (4!) necks. Tenor ended up with the high copper neck.
I used a crescent to adjust tuning on D of my JP soprano. It kind of works.