I guess they can get enlarged but it is much more common that they get split by rough cleaning, or clogged with dried finish. In my experience, the very small screw-in nozzles on Iwata and similar brands of brushes are pretty delicate. Soft stainless steel. Another problem you can have is the needle and the nozzle becoming mis-fitted so the brush cannot shoot a clean spray pattern. Iwata factory has a tech adjust the needle to the nozzle during manufacturing and he/she shoots a beautiful little pattern on paper that you get when you buy the brush. But if you bend the original needle, bump the nozzle against a hard surface, or buy a new nozzle or needle, the custom fit is down the drain and you're on your own. Bottom line is that unless you know the "black magic" of contouring and adjusting a new needle to perfectly fit the nozzle, your Iwata will probably never shoot as well as it did straight out of the box. So it pays to be very careful with an Iwata needle and that tiny little Iwata nozzle that's half the size if a grain of rice. Brands like Paasche and Badger generally use larger needles and cones (not screw-in nozzles) that are less exact but also less prone to damage. That said, I ain't giving up my Iwatas. They're just too good.