The function of PTFE is to reduce resistance and guide filament. The tube’s inner diameter is 2.5mm, and its outer diameter is 4mm. Please note that the PTFE tubes are consumables and are at risk of wear, as they may rub against the filament over time. We recommend that you check the PTFE tubes for wear during your maintenance of the machine. If the tubes are worn and not replaced in time, this may lead to feeding failures, filament accumulation inside the AMS, etc.