You can find the Surefire ProComp Muzzle Brake 5.56mm 1/2x28 here.

The SureFire ProComp 5.56 muzzle brake greatly reduces both recoil impulse and muzzle rise so that the weapon tracks straight back, which helps keep you on target for faster follow-up shots. The patented Impulse Diffusion design minimizes side blast and rear-directed concussion effects. The ProComp 5.56 duplicates the design of the SureFire SOCOM SFMB 5.56 muzzle brake, but it cannot be used to mount SureFire SOCOM suppressors. The ProComp is precision machined from US mill-certified steel bar stock. The ProComp has a black Melonite finish that provides maximum protection under harsh environmental conditions. Fits barrels with 1/2-28 muzzle threads.