This is a Safariland Shell Holder known as the 80, model 080-12.
The Model 080-12 is a Molded ABS Shotgun Shell Holder which holds two 12-gauge shells conveniently on the belt. Clips on the belt for easy-on" easy-off use. The belt clip features an extended bottom hook to keep the 080-12 secure on belts up to 2.25" (58mm) in width.
Features:
Belt mounted shot shell holder
Belt clip features an extended bottom hook
Holds two 12-gauge shells