That means two. Binary triggers use two sears and provides two shots for 2 trigger movements. Just after firing, the hammer recocks as well as disconnector grabs the hammer to limit computerized fire. Prior to the trigger is launched, a secondary sear grabs the hammer. They are an aftermarket trigger. https://binarytriggers25566.aboutyoublog.com/35852368/the-definitive-guide-to-binary-triggers