I originally posted this on Trumpet Herald, but putting this here to keep an easy record of it:
There was a discussion about Curry vs Horntrader and other mouthpieces based on versions of the Bach 3C rim. As I play on a variety of these I decided to measure all of the 3C variants I have plus a couple of others which feel of similar size, but do not claim to be 3C copies. I measured at the point where the rim ends and the cup begins. I measured three times and took the average of the three measurements. They won't be the same as the manufacturers sizings but they are like for like.
Here is the list (Outside diameter in mm first then inside diameter):
Horntrader 27.16 16.04 (based on a 3C MountVernon belonging to Arturo Sandoval)
Breslmair 3C 27.29 16.39 (rim believed to be copied from a MV 3C)*
Wick 3 26.84 16.64 (rim believed to be copied from a MV 3C)
Curry 3 27.38 16.65 (rim believed to be copied from a MV 3C)
Gewa 3C 27.23 16.62 (believed to be copied from a MV 3C)
*Breslmair modify their rims to make them match the interface diamter for the screw rim which means the "alpha angle" has likely been changed.
And some that are not claimed to be 3C copies, but are in that area:
McCann 27.63 16.08
Breslmair G 27.52 16.27
IP Brass 26.89 16.27
Kelly 4B 26.99 16.33
Alliance 2A 26.80 16.63
Sonata 4B 26.54 16.70
Wick 4. 26.74. 16.43
Alliance RM3 26.71 16.64
And some other sizes for reference:
Alliance RM1 27.04 17.26
Wick 2 26.86 16.98
What I can see from this is that the Horntrader rim is smaller than any of the 3C copies I have. As far as rim shape is concerned the Wick and Gewa (manufactured by Arnold Stoelzel in Germany) are very similar with quite a narrow rim with a flat top. The Curry rim feels wide but it is rounded and quite comfortable.
The Horntrader rim is most similar to the McCann cornet mouthpiece, both in diameter, profile and bite, but the McCann is slightly wider on the outside edge. The Breslmair G rim does not feel far off either the McCann or the Horntrader although it measures larger.
For comparison, Curry's published specs for their 3 rim is 16.9mm. I measured it as 16.64mm using my criteria, which are likely to be closer to the lip/mouthpiece interface or bite point.