Hard drives are fixed with special screws:

These screws cannot crush the rubber spacers, which is good. The installed drive sticks rather far out of the cage, so you may want to install the mainboard first.

It’s simpler with the optical drives, which are fixed in place with two spring-loaded latches:

You open them up to install a drive:

Then put the drive in and close the latches:

The only drawback of this solution is that the latch serves two bays at once.

One more drawback was found later:

If you use a standard graphics card with a larger cooler or just a long graphics card as are abundant nowadays, there is almost no space left to attach power and interface cables to the hard drive as well as to connect additional power to the graphics card.