You talk to Bruce Lee. They use a form on which you "as honestly as you can", complete the required information. From there they take a "position" on where your playing is at now...where you want it to go, what kind of horn you play, what experiences with other mouthpieces you have had, and then "dial in" what you "probably" could work with. For most people this works very well but you have to be absolutely honest when answering the questions.
In my case I was tired of intonation problems (but loved the sound) of a Dennis Wick cornet mouthpiece on my Getzen Eterna. So I got in touch with Ted Sparks and ended up buying a Sparx #4 cornet piece (GR makes cornet pieces for him using their CAD/CAM programs and machines). After a couple of months I was so happy with it that I decided that maybe they had something that would work for me on trumpet as well. I had been playing a Warburton setup but had a couple of "issues" with it. I talked to Bruce, told him the situation. He recommended the 66*** as having the rim, alpha angle, etc. most like the Sparx #4 and that would be most likely able to "take me where I wanted to go" in terms of range, etc.
I bought it. It works. No more mouthpiece swapping between 3rd parts and 1st parts. Wanna buy some Warburton bits?
