Regarding the Schilke mouthpiece numbering system, using the model 14A4a as an example:Smallest numbers have the smallest diameters. Diameter size increases as the number increases.
14 Refers to "Cup Diameter"
A Refers to "Cup Volume"A. Small - Shallow
B. Medium Small RIM CONTOUR
C. Standard - Medium
D. Medium Large
4 Refers to "Rim Contour"1. Roundest
a Refers to "Backbore"a. Tight
b. Straight - slightly more open
d. Medium Large - slightly curved out
x. Piccolo - X Large
Read the complete Schilke Mouthpiece Catalog (PDF).