Picatinny Rail
The Picatinny rail, also known as a MIL-STD-1913 rail or STANAG 2324 rail, is a military standard rail system that provides a mounting platform for firearm accessories such as scopes, tactical lights, night vision devices, laser-aiming modules and bayonets.
The rail consists of a strip undercut to form a “flattened T” or hexagonal cross-section provided with crosswise slots at intervals interspersed with flats that allow accessories to be slid into place from the end of the rail then locked in place.