How did the Parker 51 get its name?

The following article appeared in Parkergrams, Parker's internal trade newsletter, in September 1946:

The Name "51" is of Humble Origin

From time to time there have been inquiries concerning the origin of the name Parker "51". Perhaps you, too, have wondered.

Just for the record, there were three guiding stars in the selection of that name.

First the Parker "51" was put on sale experimentally in 1939, which happened to be the 51st year of the Parker Pen Company's history.

Second, we wanted to designate it with a name which meant absolutely nothing.  I believe that sub-trade-marks subtract and detract from the prime trade-mark. If we had called the pen Parker Streamliner, for example, it divides attention with our main trade-mark - Parker.

Third, the figure "51" translates into any language automatically, and because it means nothing there can be no misinterpretation. In Spanish it is the Parker Cincuenta y Uno; in French it is the Parker Cinquante et un, and so on.

I wish I could make it more exciting, but there you have it, the simple nude truth.
Parkergrams, September 1946