Putting together a top ten list of most influential pen and pencil designs in history is an easy task, because there have been a few truly standout instances where one writing instrument manufacturer puts a new idea out there and within a few short years everyone is copying it trying to catch up. The Sheaffer Balance is an excellent example, for making tapered designs fashionable. LeBouf’s pioneering use of celluloid had everyone racing to come out with pens that weren’t made of hard rubber.
And the Parker 51 is widely regarded as the writing instrument that overnight had everyone else trying to copy the solid color lower barrel, metal upper barrel look. But here’s a little secret: the Parker 51 followed in the footsteps of something else. Here’s the Parker "Duo-tone."
Note that this closely follows the lines of the Parkette on which it is based. The only differences are that the cap, rather than being marbled plastic, is in a cheap gold plated metal, with a clip that is commonly found on Parkettes:
And the lower barrel, rather than being marbled plastic, is in plain black. Note the date code, 9 for 1939:
So while the Parker 51 was one of the most influential designs in writing instruments, the Parker Duo-tone was the single most influential design for the Parker 51.