The M4SD Flash Comp optimally combines the functions of three traditionally separate classes of devices- Muzzle Brakes" Tactical Compensators" and Flash Suppressors. The M4SD II Flash Comp achieved a perfect 5 out of 5 in National Tactical Officers Association testing to achieve the rare" coveted" NTOA Gold seal of approval granted to devices which achieve perfect evaluations. Compatible with the M4SD series GATE-LOK suppressor interface the Flash Comp provides a sacrificial baffle to increase the service life of your silencer. It is also pre drilled" and 2.25" length for 14.5" to 16" permanently attached" Non-SBR" M4 carbine builds. For optimal flash reduction we recommend 14.5" or longer barreled host weapons. Extreme durability" low concussion flash and recoil reduction are the wave of the future- the Flash Comp provides an elegant solution to a complex problem. Includes shim set and over-travel stop washer (for mounting to suppressor).