Looks to be the Pantac Hydration Pack or the real piece of the gear that Pantac may have copied. Kinda looks similar to the Camelbak Pakteen but larger.
Can you provide the height of the top of the unit down to the rail, while the unit is mounted; I would like to know how much the unit will block my fov while using a red dot/BUIS.
The three screws are in a triangle pattern and I believe mounts to where the holster is mounted, the center. You can mount the light mount to Blackhawk belt paddle, strike platform, etc.