The Primary Weapons Systems® FRC 5.56 NATO Flat 3-Port Suppressor Mount Compensator for 13.8" Barrels - 1/2x28 features a 3-port design with flat shoulder and is designed to redirect flash away from your line of sight and optics for an unobstructed view. When paired with suppressors, this muzzle device boasts a tight lockup and maintains it through hard shooting cycles. Even better, a crush washer is not recommended, and timing is not required.