This is a drop leg adapter for the USGI M12 holster. The adapter allows the user to mount their holsters lower and out of the way of other gear.
Beretta M9 Holster Recommendation? - HANDGUNS - U.S. Militaria Forum
USGI M12 Holster Drop Leg Attachment [Genuine Army Issue]
M-12 pistol holster, Part #9388057, NSN 1095-01-194-3343, for a Beretta M9. USGI Manufacturer: Hill Country Leather. Fits Beretta M9 series 9mm.
USGI M12 Woodland Camo Beretta M9 Holster - Hill Country Leather - PN 9388057
Cordura Shoulder Holster
The Modular Holster Adapter: Breaking the lineage of failure
Online U.S. Army Surplus Store with Outdoor Gear, Medical, Survival and Emergency Supplies in an expansive 80,000 sqft of military surplus.
Bianchi M12 Universal Military Issue Holster
Molle 2 Holster Leg Extender
M-12 Universal Holster for M9 9mm Handgun [Genuine Army Issue]
This Military Issue M12 Holster (For M9 Berretta) is standard issue holster for the U.S. Armed Forces and has seen combat from Panama to Afghanistan
Military Issue M12 Holster (For M9 Berretta) - Devil Dog Depot
USGI M-12 Pistol Holster – KommandoStore
M-12 Universal Holster for M9 9mm Handgun [Genuine Army Issue]
USGI M12 Holster Drop Leg Attachment [Genuine Army Issue]
MOLLE II Holster / Leg Extender : Gun Holsters
This M12 holster may have seen some combat in its life, but that doesn't stop it from being one of the most robust military holsters out there.
USGI M12 Hip Holster
US Military Holster Leg Extender [Genuine Army Issue]