This is a Fobus Pouch known as the Paddle, model 3901G.
Securely carry an additional magazine comfortably. Custom retention system with exceptional fit and low profile design. Single mag pouch uses a mini paddle; capable of maximum belt widths of 1 3/4".
Features:
Lightweight compact design
Low profile design for concealability
Rubberized paddle insert for extra stability and comfort
Steel reinforced rivet attachment
Adjustable tension screw available on some models
Offered in paddle, belt and roto styles