For "clicky" retractable pens, I've seen permutations of names for the part that users press on to retract and advance the tip. Thruster, plunger, clicker, and button are all used lots of places, but among redditors and reviewers I've seen "knock" and "nock" as specific and unique terms. For reference, I saw these spellings first on Anthony Sculimbrene's "Everyday Commentary" blog, and next on "Pen Addict." I think Tony flipped from nock to knock at one point; Pen Addict is inconsistent between writers, but I'm pretty sure Brad always writes "nock." I just read a review by Mike Dudek on clickypost.com that inspired this poll. Does anyone know the etymology of these names? If you're a Parker collector, "nock" makes perfect sense: it's the name used for the rearmost part of an arrow that rests against or clips to the string. Whether you're imagining that the entire pen is an arrow, or just looking at the iconic Parker arrow-shaped clip, it works. I'd guess that this is the source for the term and "knock" is a misspelling, but my google searches are in vain. If you don't know anything about archery, "knock" describes the sound made when you push the part fairly well. I'm assuming that's why some people use the term with this spelling, though I also assume they don't know that "nock" is a real word. So, what do you all think, r/pens? What's the spelling you use? Where did you see it first?