adopted and fielded in 1995 with the designation MIL-STD-1913, dated February 3, 1995. A metric-upgraded version of the Picatinny rail, the STANAG 4694 NATO Accessory Rail, was designed in conjunction with weapon manufacturers like Aimpoint, Beretta, Colt, FN Herstal and Heckler & Koch, and was approved by the NATO Army Armaments Group (NAAG), Land Capability Group 1 Dismounted Soldier (LCG1-DS) on May 8, 2009. Currently, many firearm manufacturers include a Picatinny rail system out of factory, such as the Ruger Mini-14 Ranch Rifle. Design The rail consists of a strip undercut to form a "flattened T" with a hexagonal top cross-section, with cross slots interspersed with flats that allow accessories to be slid into place from the end of the rail and then locked in place. It is similar in concept to the earlier commercial Weaver rail mount used to mount telescopic sights, but is taller and has wider slots at regular intervals along the entire length. The Picatinny locking slot width is . The spacing of slot centres is and the slot depth is . Comparison to Weaver rail The only significant difference between the Picatinny rail and the similar Weaver rail are the size and shapes of the slots. Whereas the earlier Weaver rail is modified from a low, wide dovetail rail and has rounded slots, the Picatinny rail has a more pronounced angular section and square-bottomed slots. This means that an accessory designed for a Weaver rail will fit onto a Picatinny rail whereas the opposite might not be possible (unless the slots in the Weaver rail are modified to have square bottoms). While some accessories are designed to fit on both Weaver and Picatinny rails, most Picatinny devices will not fit on Weaver rails. From May 2012, most mounting rails are cut to Picatinny standards. Many accessories can be secured to a rail with a single spring-loaded retaining pin. Designed to mount heavy sights of various kinds, a great variety of accessories and attachments are now available and the rails are no longer confined to the rear upper surface (receiver) of long arms but are either fitted to or machine milled into the upper, side or lower surfaces of all manner of weapons from crossbows to pistols and long arms up to and including anti-materiel rifles. Impact Because of their many uses, Picatinny rails and accessories have replaced iron sights in the design of many firearms