Medium 14k Gold
1948 Parker 51 Blue Fountain Pen 1/0 12k Gold Filled cap with thin lined engraving Made in USA G/P Plain Arrow Clip with Pearl-Coloured Jewel Filler sleeve, metal Aerometric, one piece with black plastic end cap
The Parker "51" aerometrics
The MKII pens of course had a brand-new filling system that was to be adopted by virtually all Parkers in the future, the Aerometric.
Parker developed a sac in a tough plastic material, called Pli-Glass, that had a life expectancy of 30 years, but are now going on 60+. These sacs were also in a see through material which allowed one to see how much ink that was left in the pen. The sac was encapsuled inside a metal tube on which a metal pressure bar was mounted. To reveal this filling mechanism one had to unscrew the entire body cover from the section ring and back.