When your full cloned 416kit need a lighter weight of barrel or need the thread for the airsoft spec.You will need this, The HAO’s alloy barrel sets for 416A5 MWS version.This set include three barrels which represent 11″, 16.5″ (5.5″extension) ,All the barrels are CNC lathed by alloy 6061-T6 , and 4140 Steel (Extension barrel).The 11″ barrel only compatible with RS spec barrel length kit of HAO 416A5 MWS kit. And the extensions will fit most of airsoft guns which thread are end with airsoft 14mmCCW.