Requires at least 1 3/4" of rail space Small as a matchbox and weighs no more than a .45 ACP round Built-in accessory rail allows the mounting of a tactical light on the laser itself 5mW constant red beam maintains alignment through battery changes. Fits virtually any Picatinny, Weaver style, or accessory rail 1.75" or longer and has an optional momentary activation switch that comes in 6 and 10 inch cord lengths Rugged design stands up to harsh evironmental conditions; Class IIIa Laser Product: &lt;5mW power output Class IIIA laser, &lt;5mW power output