Anyone know the story behind why PC cases ended up with some #6-32 UNC screws and some M3 screws ?
I'm working on a case that takes M3 screws for the rear expansion slot covers and I'd like to think about the story every time I grab the wrong screw.
For the same reason HD's use one type, floppy's and cdrom use another. I do not know why other than just "because they could"............
and same with board standoff's...
Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun
I always assumed smaller ones require good threaded holes, while bigger ones can work by brute force making their own threads thus lowering manufacturing cost of cases - skipping additional step of tapping holes.
I'd imagine, if there is a coherent design reason at all, its more a reflection of the specifications of differing parts of computers being in the hands of different engineering teams - eg case, motherboard and more - and there being different cost/design reasons for it.
They wouldn't be thinking about the ease of use for owners, more to do with costs and straightforward options for the manufacturing process
lots of household items have seemingly random selections of screws, even those 'security' variations on torx - I've noticed some items (some kitchen equipment for instance) have such deep recesses to get at the screws, and narrow access too, that its pretty clear it isn't meant to be maintained at home with regular tools
Seems like the original PC case, 5.25 floppy, and hard drive were all #6-32 UNC. There is the occasional case that has has M3 mobo standoffs and the rare case that has M3 for the card expansion slots, but I'd say most of the cases I see are #6-32 UNC.
Then the 3.5 floppy came out in 1983 from Sony with M3 screws and the CD-ROM was also heavily Sony influenced came out in 1985 and also used M3.
So was it Sony?
I think UNC was for components with a massive body (like 5.25" FDD, HDD, usually aluminum alloy?) Screws M3 then for joints in a thin steel sheet (like CD/DVD, 3.5" FDD, PC cases). Maybe...
It could also be that the original PC being designed and made in America used a non-metric screw (since the US is the non-metric country), but the later advancements came from Japan, so a metric screw was used.
At least, that's my theory.
Normally I see the UNC screw used for the back cutouts but I suppose a M3 could be usable there. The UNC screw being larger looks more suitable for that position though.
