The 551 series is a professional, military-grade red dot sight with a long-lasting LR44 Li-Ion battery (included). The large 22mm lens provides an incredibly accurate red or green 3MOA reticle based on your preferences with several levels of brightness adjustment. The 551 series can be installed on any gun that has a pre-existing 20mm wide weaver or picatinny rail mount, no matter how powerful the gun. The durable all-metal construction is both waterproof and shockproof, allowing for many years of uninterrupted use. Each sight has an auto-off feature if it is unused for more than 2 hours, to conserve battery life. Whether you’re doing rapid-fire shooting, normal target practice or hunting in the woods, you can’t find a better red/green dot sight for your gun. 22mm x 22mm Lens. 3.9″ Length x 2″ Width x 2.4 Height. Lens Material: Anti-Glare Glass. Automatic Power Off: 2 Hours. Fits 20mm weaver/picatinny rails. APO/FPO, Virgin Islands, Guam and All Other U. The item must be in BRAND NEW Condition. No components missing i. Screws, bass knobs, plastic coverings, protective films, etc.