This is the ORIGINAl Prusa Nozzle E3D V6. We also offer an alternative 0.4mm nozzle compatible with Original Prusa 3D printers - MK2/S, MK2.5/S, MK3/S/+, and MINI/+.
Read more about different nozzle diameters and their usage at PrusaPrinters.org.
To replace your Nozzle E3D V6 please consult the assembly manual: https://help.prusa3d.com/article/changing-or-replacing-the-nozzle-mk2-5s-mk3s-mk3s_2069