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Retractable ink pens are a staple of nearly any office, and many eventually end up in homes, either through purchase or accidental (or at least I hope it’s accidental) migration in pockets from places of work. They are so ubiquitous that they are nearly disposable, and frequently given away as souvenirs.

Given their ubiquity, you might be surprised to learn that, according to Bill, the “EngineerGuy” Hammack, the original Parker retractable pen “took a team of 66 people to design.” He also notes that it’s sold “over three-quarters of a billion units” since it first appeared in 1954 and spawned several other pen mechanisms. It appears that this investment paid off!

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As explained in the video below, the pen has three basic parts: a cam body, a tubular plunger, and stop members. As the pen is clicked into writing position then retracted, the cam is forced into the desired position by two springs. How the cam body slips on and off of the stop members can be seen in a mechanical animation starting just after 1:50.

Interestingly, Parker initially didn’t put their signature clip on this pen so as not to damage their reputation as a fountain pen manufacturer. It’s not something we think about today, but this must have been a novel idea in the early 1950s, and obviously took a huge effort to implement this new paradigm. It’s exciting to think about how everyday items we take for granted today could be improved in a similar manner!