This US Nightvision Sacrificial Window is designed specifically for their PVS-7 night vision biocular. A sacrificial window protects the objective lens from damage from dust, sand, and all abrasive airborne particles. This is a particularly useful addition to your NVD kit when you find yourself in a windy or storm-like environment. These are meant to take abuse, and then swapped out for new ones, so having several sets on hand is a good idea. Keep your lenses in pristine condition with these sacrificial windows.