Part of the standard issue US Molle II system: Triple Magazine pocket 30 round. Aka, the triple M4 magazine pouch. 

These are in ACU/UCP (that grey digital camo that blends in with a gravel pit and grandma's couch) 

NSN: 8465-01-525-0598

These feature three pockets, each of which will hold a single M4/M16 magazines. Retention is provided by a top flap with a metal snap closure. They have three molle straps on the back, with additional molle straps on the front. 

These will be from a variety of makers, but all are genuine US Government issue and in excellent shape.