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.
The Picatinny locking slot width is 0.206 in (5.23 mm). The spacing of slot centers is 0.394 in (10.01 mm) and the slot depth is 0.118 in (3.00 mm).
The rail is named after the Picatinny Arsenal, which was tasked in 1992 to develop a standardized mounting system after the U.S. Army was dissatisfied with the contemporary products on the market. The Picatinny team was headed by mechanical designer Gary Houtsma. For his work in developing the rail, Gary Houtsma was later honored at Picatinny Arsenal with the prestigious Order of Saint Maurice Award.