G&P outer barrels attach to the standard G&P M16 / M4 series bodies via the usual barrel nut and Delta ring (or compatible alternatives). At its most basic, a replacement barrel can be used to vary the length of both the inner barrel and overall weapon size of your platform. Part of the charm of G&P compatible ARs is that the barrel lengths can be found from 2 to 20 inches in increments of 2 inches along almost that whole scale. This particular Stubby Outer Barrel is less than 2 inches long and will turn your AEG into a very short PDW style gun.