Picatinny rail

A Picatinny Rail is the common name for a U.S. military standard for a mounting rail system for rifles and other small arms. Formally, the specification is MIL-STD-1913, "“Dimensioning Of Accessory Mounting Rail For Small Arms Weapons”, developed at the Picatinny Arsenal and issued on 3 February 1995. It is used for accessories such as gunsights, light sources and supplementary handgrips.

There are variants with two, three, or four mounting rails. Some directly-attached accessories are mechanical mounts for classes of other accessories, such as a dovetail for optical sights, or a bayonet lug.

A related commercial accessory rail specification is the "Weaver". In general, Weaver accessories will fit a Picatinny rail, but not vice versa.