Obsidian 350D missing accessories, need help with internal standoff thread pitch

I recently purchased a 350D for my new mATX build. I started putting my components together last night and, much to my dismay, I discovered that several accessories were missing from the box. I received no motherboard screws or fans screws with the case which, according to the quick start guide, were supposed to be included.

I wasn't too upset about the fans screws as I have plenty of those, though it would have been nice to receive the black ones to keep with the all black look. I have a bunch of silver ones left over from previous builds and they really stand out against the stark black finish.

The motherboard screws presented more of an issue for me. I didn't have enough of these left over to mount my motherboard. So it looks like I'm going to have to buy some motherboard screws. It occurred to me that this is something I have never done before, as they have always been supplied with cases in the past. Does anyone know what the internal thread pitch of the motherboard standoffs is? I tried an M3-0.5 and I could pull it right out of the standoff. Haven't tried a 6-32 because i don't want to risk cross threading the standoff. I assume that 6-32 is the right size, but maybe the standoff I tried was stripped, which would be weird cause this is a brand new case. Little help please?

Did you buy the case new? e.g. tape on the box is not reapplied, protective cover for the window, tape for the front panel etc.

The standoffs should be pre-installed on the motherboard tray. If they are not there, you can request an RMA and ask for a replacement accessories box.