The Trijicon SRO (Specialized Reflex Optic) is specifically designed for pistol use. Improve shooting accuracy and speed with the wide circular field of view and clean, crisp dot making it easy for users to find and track while shooting. Every SRO has 8 brightness settings with "Lock-In" and "Lock-Out" modes and a 3-year battery life. The SRO similar to the Trijicon RMR easily mounts to popular red-dot-ready pistols, is compatible with most RMR mounts, and does not require a sealing plate. There is no need to dismount the optic for battery changes with a quick-change top loading battery. The SRO is designed to survive the rigors of slide ride pistols and is engineered for hard use. This 2.5 MOA Adjustable LED red dot is the most popular reticle size and can be used in a wide variety of pistol and other shooting applications such as target shooting.For mounting recommendations, comparisons with the Trijicon RMR, and more, check here.Trijicon SRO Features Magnification: 1x Dimensions: 2.2" x 1.3" x 1.4" Weight: 1.6oz with battery Adjustment Range: 150 MOA Total Travel Lens: Parallax Free, Tempered Glass Reticle Color - Red LED Source illumination Housing Material - 7075-T6 Forged Aluminum Batteries - 1 CR2032 Lithium Battery Battery Life - Up to 3 years of typical use Waterproof - Up to 10ft