These double stack, double magazine pouches are designed to be a secure universal fit for almost any 15/17rd double stack 9mm magazine. The extended option will increase the height of the pouch  to accomindate extended base plates and or magazine lengths asscosiated with 18/20rd double stack 9mm magazines.
 
Magazine Sizing 
Size 1
All Single Stack .45acp magazines. 
 
SIZE 2
Glock 43x/48 10rd 9mm
SIG P365 17rd 9mm
SIG P320 17rd 9mm
SIG P226 15rd 9mm
SIG P229 15rd 9mm
SIG SP2022 17rd 9mm
Smith & Wesson M&P 2.0 17/15rd 9mm - .40 S&W
Smith & Wesson Shield Plus 13rd 9mm
H&K VP9 17/15rd 9mm
FNH 509 17rd 9mm
CZ P-01 15rd 9mm
CZ P-10C 15rd 9mm
Walther PDP 15rd 9mm
 
SIZE 2 EXTENDED
Glock 43X/48 Shield Arms 20rd 9mm
Smith & Wesson M&P 2.0 21rd 9mm
SIG P320 21rd 9mm
SIG P226 20rd 9mm
H&K VP9 20rd 9mm
FNH 509 24rd 9mm
CZ P-01 17rd 9mm
CZ P-10C 18rd 9mm
Walther PDP 18rd 9mm
 
Size 3
Glock 19/17 15/17rd 9mm
Glock 22
Glock 21
Glock 41
Smith & Wesson M&P 2.0 10mm/.45acp
USP 15rd 9mm
USP 12rd .40 S&W
 
SIZE 3 EXTENDED
Glock 19x
USP 20rd 9mm
USP 17rd .45acp
 
SIZE 4
All Polymer Body Double Stack .45acp magazines. Metal body Double Stack .45acp magazines will fit slightly loose.