The 2A Armament(TM) BL RAIL Gen 2 M-LOK series has styling changes in the picatinny pocketing to match with the Balios Lite Gen 2 or Aethon receiver sets. By utilizing a titanium barrel nut"" and an innovative 45 degree mounting system"" the BL RAIL achieves a solid lockup with the upper receiver. The 2A Armament BL RAIL will ship with a 6AL-4V titanium barrel nut. An optional aluminum barrel nut is offered as a separate item for those looking to save maximum weight on a build. The BL RAIL Gen 2 is a great fit with the new styling on any quality forged or billet upper receiver offered from other manufacturers.