Apologies for the slow reportback.
Thank you very much @MJ1 for the immediate response that got me off and running with the link to the fastener kit in the Framework store:
The secondary and the main SSD screws are the same, as @David_Mellor reported. I did not measure but i think 2mm is the length; maybe 3 but less than the 4.5mm head width.
As i wrote to Framework support:
I can confirm that the main ~hard~ solid state drive and the secondary ~hard~ solid state drive use the same screw, so it must be the mentioned “Storage fasteners (Gold): M 1.4mm fastener with a T5 head, which is 4.5mm diameter and 0.6mm thick” mentioned in Framework | Fix Consumer Electronics (which i would have gotten with my two frameworks if i had known about it)
(Edited above per @jared_kidd’s correction— i hadn’t realized that solid state was not considered a type of “hard drive”; i see now that the typical phrasing is “SSD” for “Solid State Drive” and “HDD” for “Hard Disk Drive” and as for the clean, no-overlap division while it is not as if “S” stands for “soft”, modern/true SSDs don’t any spinning “disk” component either.)
I could not be sure to source a screw locally/quickly— i could not get close. This definitely does not seem to be a “pick up at your hardware store” sort of thing; checked McMaster-Carr catalogue and the Digikey site and no luck; everything is longer. A friend sent pictures of an SSD screw kit bought at MicroCenter a couple years ago (i didn’t find anything online), but the smallest was almost certainly larger (per ball point pen tip in photo for reference) than the screw i was able to easily compare it to thanks to MJ1’s tip to check the main drive’s screw.
As i happen to have ordered two Framework 16s, after exhausting other options i reluctantly(*) took apart the Framework i had already assembled that did not immediately need a secondary SSD and there was the screw right where it was supposed to be.
(* OK so i’m not the target market here, maybe, but i don’t want to be opening these up once built! Especially as i was not 100% sure the secondary hard drive would have a fastener in the one i built first; fortunately it did— if by luck i had started with the other of the two machines i’m sure i never would have even noticed the missing screw— until adding a secondary SSD there which i do expect to be doing in a few years.)
Very much hoping Framework will simply send the $9 fastener kit for all this trouble and my eventually adding an SSD to the other machine, but still in conversation with Framework support.
So, uh, my main takeaway here is if you run into any problem during assembly take a photo of the serial number on the Midplate (maybe only a thing if you ordered more than one machine?) because Framework support reasonably wants to know which machine had the issue. (I’m holding off on replying until i have the mental energy to even do that relatively small amount of disassembly again.) And maybe order the fastener kit ahead of time.