Identifying the screws to mount motherboard onto case

Just make sure that whichever screw you use projects sufficiently far enough through the motherboard in order to ensure that it has a good purchase in the standoff.

Lady Fitzgerald said:

I would have to see the screws up close and personal to be sure but my guess is if screw #2 bottoms out prematurely, it may have the wrong thread. It appears in the photo to have a tapered thread which would make it a sheet metal screw. The correct screw for mounting MOBOs to the traditional brass standoffs is a 6-32 screw and doesn't have to be very long although screws #2 and #3 both look a bit short (and the diameter of #3 looks a bit small based on fan screws usually being 6-32). Screw #1 (why do I sound like I'm hosting Let's Make a Deal?) is definitely too long. Screw #4 is probably also too long.

I just ran a 6/32 screw into a spare standoff I had knocking about and it bottomed out at a red hair over 3/16". I'm thinkin' the screw you use should be between 1/4" and 3/16" longer than the thickness of your MOBO (do not include the screw head in your measurement) to ensure enough thread goes inside the standoff to secure the board without bottoming out. If the screws you have are both too long and too short, head on down to your friendly neighborhood hardware store/home center and get the right length (I suggest you check the depth your standoffs have first; most cases use 6-32 thumbscrews to secure the side panels, btw). If you can't find black oxide, get plated steel ones and color the heads with a fine Sharpie felt pin (it actually works; I've done it before).

Edit. Ok, some posts have happened since I started posting. If screw #3's threads don't wobble around in the standoff, then it's probably the right diameter (just because it goes in doesn't always mean it fits correctly). What I said about length stands unless your illustration shows it bottomed out in the standoff, in which case that is probably the correct length.

My post has nothing to do with helping the OP, but just want to say that the above post made quite an impression on me. How many women do you know that can talk about sheet metal screws and various threads on them and make a post that long on the subject. My congratulations ma'am.

Lady Fitzgerald said:

And why should it be so unusual for a woman to know about screws? There are more of us than you obviously realize.

Maybe I just live a sheltered life. I just not have run across anyone that could carry on a discussion such as yours. :)