From top to bottom: 45 (M), 50 (XF), 180 (M/XF)
All my flighters have gold trim, and the 45 and 180 have black plastic sections (the 45's is smooth, the 180's is a great-looking crosshatch). The 50 section, being integral with the nib, is necessarily metal, but that metal has been sandblasted or ground in some way to offer a grip at the section part while being smooth and shiny at the nib part. The overall effect is very impressive indeed!
above: 50; below: 180 (M-side)
In terms of length, they are all comfortably long to write with without needing to post the cap. The 45 has the widest cross-section, followed by the 50, while the 180 is really very slim, sort of like the Sailor Daks Slim. The 45's cap closes by friction alone, whereas with the more expensive 50 and 180 models, the cap snaps closed.
I bought the 45 new many years ago for the equivalent of $16 in the transit lounge at Heathrow (it is made in the UK), and recently acquired the 180 as NOS and the 50 in mint condition, both from a "well-known auction site," for about $75 each. The 50 and 180 are both made in the USA. The 45's nib appears to be gold-plated steel, the 180's nib was advertised by the seller as 14kt gold (but there are no markings on the nib to confirm this), and the 50's nib is stainless steel, just like the rest of the section.
The 45 is the most "conventional" nib of the three, while the 50's integral nib and the 180's nib (which can be turned a hundred and eighty degrees to write with a different width) are unusual both in looks and function. Together, they show the gamut of what Parker was capable of in its heyday. The 45's M and the 180's M-side nibs are both wide, as Parkers are in my experience, both both are very smooth indeed. On the other hand, both the 50's XF nib and the 180's XF-side nib are somewhat scratchy, though the latter is slightly smoother than the former. Again, they run a bit wide -- the equivalent of a Japanese F.
Summary: the 'flighter' design is durable, streamlined, and classy. I want to enlarge my collection to include a 51, 61, and 75 flighter, if possible. Meanwhile, these three are all fun to write with and likely to last forever!
Edited by ParkerBeta, 10 December 2008 - 09:42.