With the mouthpieces which are made of stainless steel and threaded - including that one exception which is a "Symphony" silver plated brass cup/shank with rim threads - any fim fits any of the cups, but as far as the array of "donut sizes" of #2 profile rims, they range from a little bit over 32mm to a little bit over 33mm. Lately, quite a few people have been ordering the most recently added size, which is just a hair under 33mm, as far as how much of a player's lips appear inside the rim.
I don't pretend to explain others preferences, but quite a few people who previously played on (or order other of the) medium wide or one of the other narrow rim profiles, later migrate to the #2 profile after they've tried one sent from us, or maybe tried one that is owned by someone else who they met somewhere. Those who seem to not prefer the #2 rim profile seem to be mostly be those who like the wide rounded rims - such as are found on several of the Miraphone style mouthpieces.
These are very generalized trends that we've noticed with customers, and there are quite a few exceptions.
Personally, I view a few things as being humbug:
> the type of metal used in making a mouthpiece. I don't view this as important at all unless someone's allergic to a metal used to make one, or (obviously) unless it rusts - such as regular steel or something like that. The advantage I see in stainless steel is that the rims are way more resistant to being scratched, I don't personally care for scratchy rims, and I don't even care for it rims with minor scratches in them. I believe some people's whisker stubble can scratch silver or gold-plated brass rims, and I have found that setting rims down on wooden surfaces or encountering razor stubble doesn't really scratch stainless steel rims. That's why I tend to go with stainless steel rims. I don't much care about the rest of the mouthpiece. (By the way, the same amount of stainless steel vs. brass weigh just about the same.) Again, I wouldn't consider an aluminum mouthpiece or a regular iron or steel mouthpiece for obvious reasons, but one that I play on all the time (that isn't marketed) features cup/shank assembly which is made of unplated bronze (one of the harder bronze alloys, just fwiw), and that material doesn't bother me at all in a physiological way. (I do understand that many other people have all sorts of allergies.)
> I also personally view the total amount of the mass or weight of a mouthpiece is making no difference whatsoever, as long as there's enough there for the mouthpiece or its components to be stable. If you've listened to the YouTube-hosted recording of my son-in-law and me playing one of the Wilder horn, tuba, piano suites, I played that on a hyper-skeletonized version of the mouthpiece I was using at that time, and that mouthpiece had been in my possession for exactly one day. It made absolutely no difference, and I played on it because I thought it was sort of cool-looking.
I've experimented with threaded lexan shanks and threaded lexan cups screwed on to stainless steel rims, and dismissed them because the threads tend to seize (being that they are a plastic like material and not absolutely 100% stable), and also because they make a mess and clog up the the machine that's making them. (If you've noticed, the Kelly products are molded, and not machined.) I can play on lexan rims, but I'm not particularly fond of them as they are slightly "grabby". I think they're fine for outdoor use when it's cold, but I'm not one who plays very many of those types of jobs. I've been doing a Mardi Gras parade every year for the last few years, and it tends to be chilly up this way. I've used my lexan rim for those jobs, and that's about it. Minor differences in shapes are perceivable to just about all of us, and most of those have an effect on how mouthpieces work, but some of the things listed above do not.
I'm thinking that this post is already too long. I hope everybody had a great Thanksgiving.
again: This was played with a super-skeletonized version of the exact interior shape of mouthpiece that I had been playing on during that time, and the first time I used this mouthpiece was at the dress rehearsal with the pianist, and the second time I used it was at the recital:
OK...
Other than the wide array of rim profiles offered, I really try to only offer things for sale that I personally use or have used with particular models or sizes of instruments. The only exception to this is my recent outing - which was an attempt to make the "helleberg II" style/shape of cup (offered by various makers and labeled various things) something palatable to me, which it never has been. Personally, I like what I came up with much better than anything that's on the market, but I'm still not finding myself using it. I hope those who have purchased them so far found them to be an improvement over what's offered elsewhere. (Yet another one is going out today.) I was interested in seeing what I could do around that cup shape, because it's such a widely popular one, and I've always wondered if it was just me, and whether I was missing something.
(The cimbasso sound would not sparkle as much and would also be significantly more work to play were I to use a mm-larger inner diameter rim on its mouthpiece, just as one negative example of attempting to embrace the "one rim for everything" fable.)