The heatsink is an aluminium part which is used to dissipate the heat. It is a complete thermal solution. If needed for a specific application a fan may be mounted on the heatsink.
There are four threaded M2.5 holes with a pitch of 41mm drilled into the heatsink for mouting a fan. Standard 50x50mm^2 fans have hole sizes between 3.5 and 4mm and have pitches between 40 and 42mm. As the screw diameter is only 2.5mm, it is possible to mount either 42mm or 40mm pitch fans.