Vintage Parker 51 Pens - The Classic Fountain Pen
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. In the mid 1970s the Mk3 was introduced.
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.