M3 screws are the ones that should fit. There are others that are very close in size that do not.
I bought Uxcell computer "graphic cards" screws. Apart from a couple of modules that had very narrow clearances, these work great for me. I can tighten modules down by hand with a thin nylon washer underneath to stop rack rash.
I'm not sure if the link will be valid but here is the name of the item:
"uxcell Computer PC Graphics Card M3x6mm Aluminum Alloy Knurled Thumb Screws Black 10pcs"
https://www.amazon.com/gp/product/B01MTN1PNK/ref=ox_sc_act_title_1?smid=A1THAZDOWP300U&psc=1