For cylinder conversion systems, Polarstar assigns numbers to the nozzles instead of using the rifle model. This is because the nozzle length can vary between the same gun model when made by different manufacturers. This may be due to the manufacturer designing the rifle differently or the thickness of the gearbox housing affecting how far the barrel is from the jump chamber. Therefore, one nozzle length may work on different rifle models, but not necessarily on the same model from a different manufacturer. For example, a standard MP5 could require any of 4 different nozzle lengths depending on the manufacturer.

For this reason, Polarstar produces numerous different nozzle lengths to provide compatibility with a wide range of replicas. Listed below are the make and model of replicas the mouthpiece length is most commonly used with, but may be compatible with more models. For a list of replicas where Polarstar has already measured and calculated the compatible nozzle length, visit the Polarstar Help Center.

Once you determine what nozzle number your replica requires, that number is universal on all engines* that use the numbered nozzle system. So if you determine that your replica needs a #11 JACK mouthpiece, you will also need a #11 Kythera or F2 mouthpiece if you ever put a different system on it.