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