The LaserMax Guide Rod Laser for GLOCK meets or exceeds both Mil Spec and Homeland Security durability test standards (drop tests, blowing sands, temperature and humidity extremes, salt water fog, deep water immersion, 20,000+ rounds live fire). Installation is quick and as easy as field striping the weapon. A pulsing laser beam gives effortless awareness of muzzle and transcends language barriers. It can be used outdoors from dusk until dawn or indoors around the clock. All Guide Rod Lasers come pre-aligned from the factory at 20 yards. It will never come out of alignment and there is no need to re-zero after battery changes. As close to the bore of a GLOCK as possible, positioning allows for the closest and most consistent relationship between your point of aim and point of impact (POA/POI) over all shooting distances. Ambidextrous controlled activation is in the custom take down lever that very closely resembles the factory GLOCK take down lever. This model emits a green laser. Made to fit Glock models 20/21/41 GEN4.