During a scene in Star Trek: Discovery season 3 episode 6 "Scavengers", Burnham mentions self-sealing stem bolts. This item has had a few mentions in earlier Star Trek series, beginning with DS9. It seemed to me that prior mentions typically occurred in scenes having a lighter sometimes comedic tone. This leads me to ask: is it a writer's in-joke, or perhaps a signal to not to take what is happening on screen too seriously?
From Memory Alpha which is sourced from DS9 companion book.
Story-wise, stem bolts were quintessential MacGuffins, with a name that was pure technobabble. Peter Allan Fields, who "invented" them, admitted that he didn't have "the foggiest idea" what they were used for. According to Ira Steven Behr, the writing staff used them long after Fields' departure from the series as a tribute to the former producer. (Star Trek: Deep Space Nine Companion, p. 52)
It appears so. According to Cirroc Lofton and Aaron Eisenberg (Jake and Nog) speaking on the 7th Rule DS9 podcast, just getting their tongues around the words "Self-Sealing Stembolts" initially caused much difficulty, to the great annoyance of director Les Landau, after that it became a recurring source of humour on that podcast.