Asus
MSI
Gigabyte
DFI
So far, only the asus has 2 slots in between the PCI-E slots, so I guess that is why they used it, but I dont see why this thing cant be made to fit other motherboards. When you were saying small differences in spacing, I thought you meant that the distance between the PCI-E slots could vary by minute amounts, even if there are the same number of empty slots between them.