This weight bag is designed to help counter-balance the weight of your ANVIS NVG mount. It reduces neck fatigue, which helps you stay alert during a mission. The bag is perfectly sized to fit on the 3" x 2" stock hook and loop on the back of HGU/56-P, IHADDS, and SPH-4 helmets, beneath the ANVIS battery pack. Constructed from 1000 denier water repellent Nylon Cordura. Dimensions Empty: 5" x 2.25" Dimensions Filled: 4.75" x 2" NOTE: Maximum size of prefilled weight for this weight bag is 22oz. While all of our prefilled weights will fit into the Large NVG Counterweight Bag, it is specifically designed for the 16, 18 and 22 ounce weights.