This is what 2A Armament says:
 
 
The 2A Armament™ 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.

Note: If you have an earlier Balios Lite receiver set you will want to use the first generation BL RAIL M-LOK series.  See pictures for differences.

Features:

    Made from U.S.A. Certified 6061 Extrusion
    U.S.A. sourced 6AL-4V Titanium barrel nut as standard
    M-LOK mounting solution
    Mil-Spec hardcoat black anodized
    Free floating design
    1.3” Internal Diameter
    7” Rail with Titanium nut (weight 5.7 oz)(2A-BLRML-7G2)
    10” Rail with Titanium nut (weight 7.1 oz)(2A-BLRML-10G2)
    12” Rail with Titanium nut (weight 8.4 oz)(2A-BLRML-12G2)
    15” Rail with Titanium nut (weight 10.5 oz)(2A-BLRML-15G2)
    1-5/16” crows foot tool or premium armorers wrench recommended for installation (Not Included)