This is a Spike's Tactical Brake known as the Dynacomp chambered in 556NATO, model SBV1017.
The Spike's Tactical Dynacomp is designed to reduce recoil impulse and muzzle climb to provide faster follow up shots. The Dynacomp accomplishes this by balancing the direction of the blast along the vertical (upward) and perpendicular planes of the muzzle to lower muzzle rise. The ports on the Dynacomp are ball dimpled for smooth expansion of gases and rapid heat dissipation. The front of the device is 0.25" thick to better handle the abuse of full auto fire.
Features:
416 Stainless steel
1/2X28 thread pitch
Ball dimpled expansion ports
Black nitride finish