Hot runner nozzles are the link to the cavity. They either directly gate into the part or into a sub runner which will lead into the cavity. Sprue Bushing / Single Nozzle Viscosity of melt High >150 Pa's: PC, PMMA, PEEK, PES, PSU, PEI, POM Medium = 60..150 Pa's: ABS, SAN, ASA, PBT, PET, POM (Copo), PA, PPE, PPO, PPS, PC/ABS, PC/PBT Low <60 Pa's: PP, PE, PS, LCP, TPE