And then the cooler is mounted on the CPU using the back-plate:

There are two holes in each leg of the back-plate so that it could be used on Socket AM2 as well LGA775 mainboards. The back-plate has a sticky multilayer pad that prevents the contacts on the reverse side of the mainboard from closing.

The Fourier IV looks like this inside a system case:

The mounting holes around Socket LGA775 being symmetrical, the cooler can be oriented in any of the four possible directions. I installed it in such a way that the ends of its pipes faced upwards. Note that this orientation of the cooler is only possible due to the Thermaltake Extreme Spirit II cooler installed on the chipset. If the standard passive heatsink or a cooler like Cooler Master Blue Ice Pro were installed on the mainboard’s chipset, it would get in the way of the pipes and the Fourier IV would have to be oriented differently.

Moreover, the cooler’s heatsink is tilted downwards and the fan is a mere 5 millimeters away from the power coils and capacitors in the mainboard’s near-socket area.

If some elements were taller or had heatsinks, there would be problems installing the Fourier IV on the mainboard. Perhaps the installation would be absolutely impossible.

Despite its larger dimensions, the Spire Fourier III is less fastidious in terms of compatibility.

There is over 3 centimeters from the mainboard surface to the bottom of the fan of the Fourier III.

I don’t know the recommended price of the Fourier IV and III coolers but they are selling for no more than $50. The manufacturer recommends using both these models in passive mode (i.e. without a fan) on CPUs with low power dissipation.