Originally Posted by
Mitsu3000gt
Standard mobo screws are #6–32 x 3/16″ or M3 flat head. It should be in your manual somewhere, but some manuals are pretty bad haha. Usually there are standoff screws you need to screw into the case first, then your mobo screws into those and not directly into the case - that may be causing you some confusion.
#1 most common mistake is not putting on the I/O shield before installing the mobo, and it's super annoying to fix. Some mobos now come with a fixed I/O shield but it's not super common.