ZERO flash. Nada. None. These particular units are part of a contract overrun, and are parkerized (instead of our usual black oxide coating) and are also designed to use the HK flash hider retaining spring. These will mount right up on any standard 1/2x28 threaded gun. HK Spring and crush washer not included. Designed specifically for .223 caliber (and 5.56 too, of course...) weapons with a 1/2x28 tpi muzzle thread the MA-6450 Eclipse Flash Hider does not just reduce flash, but rather eats it up entirely leaving nothing but inky, black night when shooting. Both in internal and independent testing, we and others have not found a single brand or bullet weight of ammunition that produces any sort of flash with the Eclipse Premium Flash Hider. 55 grain XM193, 75 grain Privi Partizan, even your crap 55 grain Wolf Military Classic- the only way you know the rifle was fired is from the noise! Manufactured from 8620 steel, heat treated, and then parkerized to create the most durable part possible, the Eclipse is the most effective flash hider currently available for the AR-15 and M-16, SIG 556, or any other weapon that fires the .223 round. The Eclipse Flash Hider is marked "MA" and "223" to denote that it is made right here in the USA by Manticore Arms for .223 caliber weapons. It is 2.25" long, weighs 3.6 ounces, and is a standard 22mm diameter allowing for the use of most standard NATO muzzle accessories. PLEASE NOTE: The MA-6450 Eclipse is only meant for projectiles .223" (5.56mm) in size or smaller. Do not mount this on any weapon firing a larger projectile as the projectile will not clear the bore of the muzzle device! Some barrels are threaded for 1/2x28 but fire a larger projectile, ALWAYS check what the barrel fires before installation. Additional models of Eclipse will be available in the near future to accommodate other calibers and thread patterns.