This is a Magpul Industries Accessory known as the MOE Illumuniation Kit, model MAG402-BLK.
The MOE Illumination Kit includes everything needed to mount a 1913 Picatinny rail compatible weapon light to a MOE Hand Guard or Forend. The four-piece kit includes a short rail section" cantilever rail mount" two Surefire(R) optimized pressure switch pad mounts (both old and new styles)" and all mounting hardware.
Features:
Kit is specifically designed for MOE and ACR Hand Guards and is NOT compatible with other makes
