CoolerMaster Case PCI slot screws?

I made the mistake of purchasing a CoolerMaster case for my first build. I don't like it. It has a very cheap 'feel', with awful fit and finish. Anyway, the 'tool-less' PCI card holders do not overwhelm me with confidence. I would like to add a screw in the screw hole to secure them. Problem: none of the supplied screws fit the PCI slots. Would anyone know the specific screw size to buy? Many thanks.

Every low-end CoolerMaster case I've bought has had problems, although typically minor. Usually, screw holes aren't properly tapped, but forcing the right screw in just once fixes it. The tool-free drive mounts aren't really secure. OTOH, my RC-690 is an outstanding case. At the low end though, I've switched to Rosewill, and every one of them has been just fine. Consider the $625 SBM article though, and add a front 120mm fan if you go for a high oc in one. The modest oc I do is fine in them.