Standoffs

The nine raised dimples are the built-in motherboard standoffs for full size ATX motherboards.

The other threaded holes are for add-in standoff posts for use with motherboards that don't fully conform to the full size ATX motherboard form factor.

Ah, thanks for explaining that. So I can use the built-ins for the board I'm putting in,
which has just 6 screw holes and seems to fit with the case layout. Likely no need
for additional standoffs?

If the mounting holes on the motherboard correspond exactly with the raised dimple standoffs then you'll be fine.

The problem arises when the raised dimple standoffs don't match with a mounting hole on the motherboard and that is when it can cause a short circuit on the underside of the motherboard.

In fact, the mobo should be fastened to the case ONLY at the places where the mobo has holes for it. The mobo is designed to contact Ground at those points. It should NOT contact the case anywhere else, as ko888 has indicated. So you should NOT add extra standoffs at other spots.

thanks all for the replies. Being my first build, I was completely ignorant how the mobo should be properly mounted. I had
assumed that the built-in standoffs in the case were all I needed. I mounted the mobo to those originally. The PC would start,
then shutoff after a few seconds. I installed brass standoffs into the built-in standoffs on the case, then mounted
the mobo to the standoffs, and the PC fired up and stayed on. I was able to install the OS and all appears to be running smoothly.

thanks again!

Mike