Kanstul Mouthpiece "Bb-C"... What is it?

[hduong]

Have you tried emailing/calling Ziggy or Jack at the factory?

[iiipopes]

Or Jim, who works directly with the mouthpieces?

Does it look like a Bach 18? If so, it may be their version of an 18, which you can find the specs here:
http://kanstul.com/mouthpiece.php?PmIns ... ne%20Piece" target="_blank

I like the 1.28 rim diameter rather than the stock 1.26 diameter of most 18's and clones, so Jim made me a custom mouthpiece with these basic specs except for 1.28 rim i.d. It works great with a wide flare bell or a souzy.