I noticed that no one actually mentioned how to remove the Parker Frontier's ink feed and nib, and someone actually suggested that it was friction fit. I just took one apart yesterday after I accidentally bent one of the tines, and realised that the ink feed can be unscrewed (counter clockwise), much like the Sonnet.
Interestingly, although the ink feed does not fit the Parker Sonnet, the nib does (or at least, the relatively modern type steel nib/feed). All it does is to coax the nib out (which is clipped rather tightly onto the ink feed), do the same for the other and swap the nib. This would be an easy solution for people who complain that they prefer their Frontiers to Sonnet nib, yet preferring the Sonnet pen body/balance. Right now my Parker Frontier has a fresh stainless steel Sonnet Fine nib on it, and works perfectly well.
I am surprised that no one pointed this out yet (after doing a quick search in the forums), but well, I could be wrong!
Edited by Limenweim, 27 October 2011 - 02:08.