The more round unpainted base crimp looks similar to an Asian filter like Full, NPN etc. Also the plastic base cover isn't seen on US filters that I know of, and the o ring gasket with edge is not found on US filters I know. I call the crimp Asian because I think they buy the same machines. American crimp, as I call it, is flatter, more even with the can side. I like the flat crimp for no other reason than, to me, it looks more developed.