MIL-STD 1913 Picatinny and NATO STANAG rails
MIL-STD 1913 Picatinny and NATO STANAG rails -- The Picatinny rail, or Pic rail for short, also known as a MIL-STD-1913 rail or STANAG 2324 rail, is a military standard rail interface system that provides a mounting platform for firearm accessories. It was originally used for mounting scopes atop the receivers of larger caliber rifles.