At first I thought it might have been made this way to accommodate someone's logo to be soldered on there, but it has no solder tinning; it's gold filled, and it has an impression of the vertical arrow shaft running through the area that usually would have the feather impressions, so the feather impressions were not ground off or there would not be this vertical shaft; it would have been ground off, too.
0 ITEM #5120: PARKER VACUMATIC DESK PEN WITH FLEXIBLE ACCOUNTANT NIB.
It should be noted that some double jewel examples have been found with the imprint up by the clutch ring, with a datecode of “1”.
In addition, I have been able to inspect a demonstrator with the “1” imprint by the clutch ring and a rounded blindcap.
When one thinks of the vintage Parker 51 pen, one generally has in mind the Aerometric Mk1 as illustrated below with the short arrow clip and rounded end to the barrel.
This model, with many variations, was in production in the USA and UK from around 1948 to the late 1960s In 1969, Parker UK introduced the Mk2 which is most easily distinguished from the Mk1 by having a squared off end to its barrel and a Parker 61 type clip. The Mk1-3 classification of the Aerometric 51 is useful as a guide, but is a great simplification as design changes, driven both by technological improvements and the need to reduce production costs, came about throughout the 51s production period.
This nib had two identifying stars (very much alike those on the famous "star clips") these nibs came in eight different styles, all denoted by a letter: A Superfine, Rigid, Long nib.
During the first quarter and part of the second quarter of 1942, the imprint remained all in one line, just as the 1941 pens; Parker “51” Made in USA Some of these pens will incorporate early production materials, such as the caps and speedline filler.
They can be easily distinguished from later production by several unique characteristics.
Practically all pens of this period are double jewels, meaning that they have a decorative “jewel” at the top of the cap and at the end of the barrel (a handful of single jewel pens dated 4th quarter 1941 with imprints by the clutch ring have been found).
Double jeweled, triple band, Medium 14K nib and a super clean (uncorroded) lock-down filler.
This has a rare clip in that the back end is flat, with no feather impressions.
#5: A two-tone gold and platinum "USA Parker" nib used on the topline pens until 1936.