This is what 2A Armament says :
 
 
The X4 brake is a muzzle device for large bore applications. The X4 was developed with a large initial chamber that provides a reactive surface for gasses to mitigate recoil. The secondary chamber provides some compensating effect. The X4 was tuned to provide a softer felt impulse over traditional brakes.  The X4 is a welcome addition to any large bore rifle.

Features:

    7.62mm/.308 caliber or smaller applications
    Made from U.S.A. Certified 4140 bar stock
    Blasted and black phosphate coated
    Threaded 5/8 x 24 TPI for common applications
    Length: 2.75 inches
    Weight 3.0 oz
    Product of Idaho, MADE IN THE USA
    SKU (2A-BRAKE-X4)