Do the Pelikan 450 and the 600 City Series pens have the same nibs? If so, is the nib the same size as a normal 600 nib? Thanks in advance!

I´ve read somewhere that the 4xx and 6xx series have the same threads in the nib assembly, so that they can be interchanged; however, the 600 nib is slightly longer and you could have problems with capping the pen.
I haven´t checked this out, but the 600 nib does look a bit bigger in this photos (which I think I plucked from the Pelikan site):

The M620 Cities series pens have 18K nibs, while regular M600s have 14k, but the size is the same.

Thanks SaintSimon and Rique. I know that the 400 nibs fit the 600s fine, but Richards site says the 600s don't fit the 400s - and I'm guessing you're right Rique about the nib length. The reason I asked is that Pam Braun said that the Concorde City Series has the same nib as the 450, which is the same length as a 400, and I was wondering how that would work - she may have meant they are both 18k rather than that they are the exact same nib though. Thanks guys.