A flash hider is a muzzle attachment for a firearm used to quickly disperse the burning gases emitted from the barrel so as to limit the amount of flash seen by the shooter.
Not only do they serve a purpose, but they also give your AR a custom look.
Recommended torque is 15-20 ft-lbs, the use of a crush washer is also recommended. 1.75" overall length.
22 Cal - 1/2x28 DO NOT USE ON 9MM
30 Cal - 5/8x24