In essence, this is correct. However, it should be noted that the ATX standard has always left some freedom of form and position for the motherboard. The most typical situation is that the board has to be provided with a metal plate (usually 1 mm thick) which is then attached to the case with nuts and bolts.
However, if the plate is not present (and in many cases, it simply isn’t), you can still fit a motherboard in an eATX case. In theory, it should be noted that this is wrong from a theoretical point of view. But it works fine anyway.
The majority of eATX cases have 1.6 mm (0.06 inch) holes on the motherboard mounting plate in the same positions as ATX motherboards place their mounting holes, so you can use a regular ATX metal plate to fasten a standard ATX case to the eATX case. Most eATX cases also have 20 mm x20 mm square mounting holes in positions that correspond to those of ATX cases. You can use these to mount a board without a plate, as long as you match the original holes from the eATX case with those of your motherboard.
In some rare exceptions, eATX cases have no standard mounting holes at all and only have 3×8 or 4×12 holes. In such cases, you should use standoffs (see below) to mount a standard ATX board into an eATX case.
The motherboard mounting plate of eATX cases is typically connected to the rest of the case by three screws (in most cases), so these must be removed from your case if you want to fit a motherboard to it. The plate is usually attached sideways, so the screws must be removed from both sides.
If you are using ATX standoffs
Remember that they must go into the mounting plate of your case and not directly into the case itself. Since eATX cases don’t have an intermediate plate between motherboard and case, you have to use standoffs.
If the eATX case is of an older model, then the motherboard mounting plate may not be a single metal sheet. In this case, don’t try to screw standoffs directly into your board through its holes–they will probably break. Instead, use nylon screws for attaching the standoffs in your case:
If your eATX case has no holes (or you don’t need them because you want to use standoffs), it is important not to drill too big a hole for the standoffs. The total diameter of the standoff should match the board’s holes so that they fit exactly. Holes with larger diameters will allow the board to rotate.
Therefore, you should cut the standoffs and then file them smooth with a nail file or similar. A final touch can be given using a metal file. Since eATX cases don’t have an intermediate plate between motherboard and case, you have to use standoffs.