I'm building a computer. I might be able to use an old case I have, but I don't have any screws for (I assume) just the hard drive and motherboard (I have fans that will come with their screws). What type of screws do I need, or what do I need to know to know what type of screws I need?
Take a old one out and take it to the shop is the easist way to get the correct screws that you need.
'The shop'? If you mean an electrical store or PC shop, I'm sure there are easier ways than walking a mile carrying a case to a town centre that has neither of these.
Motherboard screws(presuming you need stand offs) HDD/SSD mountings screws Mixture of both screws if you don't need stand offs
If you put up a post in the marketplace then I'm sure that someone will have a few spare screws that they can send your way. Work out how many you need and ask nicely and I'm sure someone will have some going spare You'll need motherboard standoffs (to prevent the board from shorting out against the metal of the case), screws to attach the board to the standoffs, screws for the drives (HDDs/SSDs and optical drives) and possibly a screw or two to attach PCIE card brackets to your case. Hard drive screws and those used to secure expansion cards tend to be 6-32 and optical drives tend to be M3. Fan screws are self-tapping but it sounds as if you have these covered already. See here for a bit more info...
