This is a Sticky Holsters Mag Pouch/Light Holder known as the Mag Pouch Sleeve, model MPSP1.
The Mag Sleeve is a IWB or Pocket magazine or accessory holder. This can be used to carry a full sized or double stack magazine" flashlight" tourniquet" etc.
Features:
Ambidextrous
American Made
Latex and allergen free
Multi-Use and Multi-Fit