MK8 0.4 mm Nozzle for the MakerBot Replicator 2 3D Printer. MK8 nozzle represent improvement over previously used MK7 nozzle. The main difference between the MK8 Stepstruder and the MK7 is the ratio of melted to unmelted plastic inside the heated nozzle. You don't want PLA to stay melted for too long, because it will start to degrade, but the new design should eliminate that problem. About the same amount of plastic fits into each nozzle, but in the MK8 nozzle, more of that plastic remains solid. That means that any given bit of PLA will spend less time sitting in the heated nozzle in it's liquid state, and won’t have much time to degrade.