Part of the standard issue US MOLLE II system: the ubiquitous double M4 pouch.
These are in OCP
They fit two M4/M16 magazines grenades.
NSN: 8465-01-641-9431
They feature a Velcro closure flap with two MOLLE straps on the back. There is an internal elastic loop to help with magazine retention.
These will be from a variety of makers, but all are genuine US Government issue and in excellent shape.