Defintely my favorite tenor mouthpiece, what does the M0 on it mean?

This html message parsed with html2text ---------------------------Medium Open referring to the tip opening. \\--- tnasaxman@yahoo.com wrote:
From: "tnasaxman"  To: MouthpieceWork@yahoogroups.com Subject:
[MouthpieceWork] Chedeville Tenor mouthpiece Date: Thu, 01 Mar 2012 21:00:34
-0000 Defintely my favorite tenor mouthpiece, what does the M0 on it mean? * *
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